Our new Thunderbolt cranks are shipping now. Some aesthetic updates to the previous Twombolt crank should be immediately clear, but the biggest improvements have been made in the manufacturing stages.

Unlike ordinary heat-treatments, which are often merely an after-thought, The 41-Thermal® process encompasses all stages of production, and includes our own joint preparation controls, refined welding techniques (now visible in the crank’s larger weld beads), and of course, in the post-weld heat-treatment system that we originally pioneered in 1999 and continue to refine and tweak to this day.

• Laboratory tested and team proven
• Updated open-ended spindle cap
• New wedge cluster band with greater flexibility
• Never-Wobble crank arm and spindle interface guarantee
• 41-Thermal® lifetime replacement warranty against bending, cracking and breaking
• US Pat. Nos. 7,267,030, 7,523,684, 7,523,685, and/or 7,770,492
• 1 lb. 11.8 oz. (788g)
• 175 or 180mm
• RHD or LHD
• Available now in Black, White and Limited Edition Colors

For the first time, we have decided to share how we lab test our cranks…

Our proprietary Stampy testing rig is designed to mount the cranks in a way that is as true to real riding conditions as possible. All of the cranks are mounted in bottom bracket bearings with spacer tubes and arm spacers, just as they would be on a bike. To test the arms, special high-strength spindles are used in place of pedal spindles, which are then loaded directly on the centerline of the pedal.

The standard lab testing machine only applies a load of up to 2000N (or 450lbs) in this test. For most bicycles this would be fine, but BMX obviously requires much more. To push it beyond the normal requirements, the Stampy arm has been designed to magnify the applied load by utilizing a simple lever. This unique rig design can take the test load up to half a ton per cycle.

In the video you can get an understanding of how 4000 Newtons, or 900 pounds of force per pedal, can flex and bend a crankset. Many cranks deform so heavily that if you were riding them on a bike they wouldn’t clear the chainstays any more. To put it in perspective, this is the amount of force that a 180 pound rider would apply to the pedals if they were to hit 10g’s on impact.

As you have come to expect, we continue to take development and engineering seriously. As such, we’ve made massive gains in strength without adding a single ounce of material to the original product’s design. While lab testing allows you to quantify a product’s performance, replicating it in the real world is just as critical. This is why our team riders rode the Thunderbolt cranks for well over a year before they were ever available in stores.

We hope you’ve enjoyed this special product testing video and we’re confident that you’ll appreciate the Thunderbolt as much as we do.

Thanks.

We have a very limited batch of JCPC pedals that are currently out on the market and we expect to get more by the end of the year. If you’re one of the few to get a pair, here’s a fully detailed instruction manual to go along with it.

New “Socket Drive” Interface

This 9-sided sprocket interface has been designed as a new standard for sprocket fitting. It can be built into the spindle on 2-piece cranks like the Twombolt, or it can be incorporated into the arm on 3-piece cranks.


A new interface seemed to be a necessary development because sprockets have become smaller across the board. On anything less than a 25-T there starts to be a heavy concentration of stress around the drive bolt and the sprocket teeth. Switching to a closer spaced sprocket bolt is one solution, but that also increases the stress on the sprocket as the same torque applied at a closer radius results in a much larger contact force.

This new feature eliminates the need for a drive bolt altogether, which saves weight and simplifies the entire assembly process, as well as removing a potential weak spot in the crank arm.


The Socket Drive interface size is big enough to let a 22mm axle pass through in the case of 3-piece crank designs. Nine sides were chosen because an odd number of sides allows the sprocket to self-center, so the sprocket can be a relatively relaxed fit on the interface rather than needing to be a interference fit to ensure concentricity (as it is on the standard Twombolt crank).

Nine was chosen over “seven” sides or “eleven” because ultimately the engineering numbers look good. As the number of sides increases the fit becomes more critical, making manufacturing and assembly harder. As the number of sides decreases, the inefficiency of the interface overall decreases and the weight increases. The nine-sided Socket Drive interface also eliminates the need for the steel insert that might be necessary with a splined interface, which helps keep everything simple and affordable.


Sprockets down to a size of 10 teeth are theoretically possible (though lets hope things never go that far) so this means the interface should be “future proof” too.


If you’re a manufacturer that’s interested in using the ROYALTY FREE interface, please download the spec sheet for dimensions and tolerancing specifications and feel free to use the drawing to produce your own Socket Drive sprockets. Dimensions for making the crank’s sprocket boss will also be posted soon.

Matt Beringer e-mailed us a bike check today along with a couple of photos. With winter coming to an end, it looks like he’s getting his bicycle dialed for the warmer days ahead. Aside from a couple parts here and there, he’s pretty much taken apart his whole bike, for one thorough overhaul. Click the pics to make ‘em big.

FRAME: S&M Dirt Bike 21.25 FORK: S&M Pitchfork XLT STEM: S&M Redneck XLT BARS: S&M Beringer XLT HEADSET: FSA Internal GRIPS: Odyssey Beringer, no flanges LEVER Odyssey M2, Medium (the gyro cable one) BARENDS: Homemade 6 shooter ones CRANKS: Odyssey Twombolt, 175mm SPROCKET: Odyssey Million Dollar Sprocket, 28t (with half the inside guard cut off) CHAIN: KMC 410H black PEDALS Odyssey Cielincki, Magnesium PEGS: Odyssey JPeg Lighter (rear), old Odyssey Ti. front WHEEL (FRONT): G-Sport Marmoset hub laced onto Odyssey 7K 36 (black anodized) WHEEL (REAR): G-Sport Ratchet w/10t driver laced onto G-Sport Rib Cage 36 (black anodized) BRAKES: Odyssey Evo 2 GYRO: Odyssey SEATPOST: Generic pivotal SEAT: Generic pivotal couch SEATPOST CLAMP S&M TIRES: Odyssey Aitken, Plyte Street (1.9 rear, 2.25 front) HUB GUARD: Homemade CHAIN TENSIONER: Homemade BOTTOM BRACKET: S&M press fit

Ride BMX has a couple video how-to’s with Mr. Jim Bauer. The first one is how-to install a bottom bracket and the other one is for our Odyssey Twombolts (embedded after the jump). If you’re looking for a printable version, click HERE.

Oh and if you want to get a little bit more info about that Terry Adams cover shoot we posted yesterday, there’s a Q&A over at the ESPN site.

We released the G-Sport Ratchet Hub a couple weeks ago and we now have an instruction manual available for download. It has step-by-step instructions for maintenance, cleaning and switching from right to left hand drive. In it, you’ll also find a complete listing of technical specifications for the hub.

TWOMBOLT CRANKS SHIPPING
Our update to the Wombolt crankset is on its way to shops and distributors. Twombolts (Two+Wombolt) are available now in fluorescent red, white and black. We have RHD-175 at the moment, with LHD and other sizes following soon.

The new features for the crank are as follows:
- Updated mating arm lug for improved fit and increased durability.
- All-new cluster design that optimizes the arm’s interface, simplifies assembly, and makes use of a durable AND replaceable elastic retainer band.
- Greatly improved overall function and performance proven both in the lab and during extensive long-term riding.
- 2 lbs. 2.5 oz. / 978g (with Mid BB). 1 lb. 13.5 oz. / 836g (without BB).

New Twombolt mating arms and wedge clusters are compatible with existing Wombolt drive arms (click to enlarge).

NEW INSTRUCTION SHEETS (CLICK TO ENLARGE):

1. Slide the sprocket onto the spindle.

2. Lubricate the sprocket bolt threads.

3. Start the sprocket bolt in the crank arm threads. Do not fully tighten it down. This step helps to keep the sprocket properly oriented in the following step.

4. To seat the sprocket, place the spindle in a bench vise and gently tap the crank arm using a hard rubber mallet. Use wood to protect the sprocket. Snug the bolt into place after fully seating the sprocket.

5. Check for the proper bottom bracket spacer tube size by holding the assembly up to the frame’s bottom bracket shell.

6. Prep the bottom bracket shell with light grease.

7. Use a bottom bracket press to fully seat the bearings. If a press is not a available, a make-shift version can be made by using two plates (old wood, sprockets, bearings, etc.) a bolt, a nut, etc.

8. Note the fully visible and properly positioned spacer tube in this photo. This spacer tube should always be used.

9. With a 6mm (1/4″) sprocket and a Mid BB, use one of the thick (3mm) spindle washers to achieve proper chain alignment. Adjust this spacing as necessary to accommodate any variation with the BB and sprocket size.

10. Slide the spindle all the way through the bottom bracket bearings. The spindle should slide through with only a very gentle amount of force if the bearings have been fully seated in the frame’s BB and are manufactured to the proper 22mm inner diameter specification.

11. Note the thick spindle washer (3mm) between the 6mm sprocket and Mid BB.

12. Slide the included spindle washers on. The spindle washer diameter allows the crank arm to move past the wedge cluster, so be sure to back the wedges up against at least one of them.

13. Use enough washers to cover the spindle’s “step” between round and hexagonal by at least 1mm.

14. Only the spindle’s hexagonal flats should be visible after the washers are installed.

OPTIONAL: Most aluminum dust covers can be used. However, you should be sure to use at least one of the included spindle washers between the dust cover and the wedge cluster. If there is not enough room for this, stick with using the washers alone.

15. A gentle amount of force will allow the new elastic cluster band to expand for installation on the spindle.

16. Slide the wedge cluster into place.

17. Flip each individual wedge up and apply anti-seize to the spindle’s hex flats.

18. Lube the spindle threads.

19. Lube the wedge faces that contact the arm.

20. Smooth the anti-seize over the entire wedging face.

21. Push the crank arm onto the wedges.

22. Use anti-seize on the lip where the locking bolt contacts the crank arm.

23. Lube the lock bolt threads.

24. Tighten the lock bolt as needed with an ordinary “long” 6mm hex key wrench (shown).

25. Check the sprocket bolt tightness.

26. The cranks should spin freely in the bottom bracket if you’ve done everything properly. For additional tips and information, please check the instruction sheet included with the crankset.

This month I want to continue where I left off last time. If you remember I had just finished assembling the worlds most garish wheel, a lovely little rear 48, laced 4 cross and interlaced under the third. But there is a lot more to wheel building than just putting the parts together in the right order. Wheels are very simple, they may look a bit complex, but like all the best ideas they have been with us so long because they are simple and work. Unlike the Government (which seems to think that it makes more sense to continue to pour money into a disastrous policy of smashing apart the very building blocks of the universe to get energy rather than make a small effort to pioneer profitable technology to harvest some of the freely available energy around us in the waves, wind and sun) we can make the most of this simple technology by putting in just a little more effort.

If you hunted out a magnifying glass and built a wheel following last months pictures then you should have ended up with a nice wheel but when you first rode it it will have made quite a lot of “settling in” noises. Little “tings” and “pinks” will have followed you down the street for the first ride and you would soon notice that the spokes had become a little loose and it would need re-truing. Worse than this, if you ride the wheel too hard before it has had a chance to bed-in, there is a higher chance that you will damage the rim or break spokes before the wheel has reached full strength. Any flatspots in the rim acquired now will be with you forever. Remember that most of the wheels strength comes from the spokes, if these are allowed to get too loose the rim alone has very little hope of standing up to even the most gentle riding.

So what is this “bedding in” ? Well, you have probably noticed by now that spokes are relatively hard steel, while most hubs are softer aluminium. If you look at an old hub you can see the marks where the spokes have pulled into the hub flange and made themselves little grooves to sit in. This is quite normal and nothing to be worried about but as it happens the spokes move outwards very slightly and this is equivilent to loosening them off a few turns. You might think that this bedding in happens gradually over the entire life of the wheel but a large part of it actually takes place very early on. As a curved spoke sits against the aluminium of the hub shell it only contacts on a very small area so the force becomes a very large pressure. So like a foot in mud it sinks in slightly. But as the spoke creates a groove, the surface area that the force is spread over very quickly increases so the effect slows right down.

The best wheel builders know that you can reduce these effect and make a stronger longer lasting wheel by “wrestling” with it a little after the build, to artificially bed the spokes in.

So picking up from last month, lets assume that you have just built your new wheel. You have inserted and laced all the spokes and have just finished going round the wheel adding the same numbers of turns to every spoke to get the basic tension on. Hopefully, if all has gone to plan, all the spokes are all at a similar tension and it is pretty much true.

With a few minutes of extra effort we can simulate the first few hours of riding without the risks of a heavy landing damaging the rim.

The first stage is to help the crossings settle to their best alignment. To do this simply squeeze the spokes together on one side of the wheel. Grab two “crossings” and squeeze them hard together. The harder the better, you should be able to feel the spokes REALLY digging into your hand. Try not to draw blood but don’t hold back on the wheels account. Work your way around the wheel squeezing like crazy. Go round at least twice. If the wheel noticeably loosens off then go back to the wheel build stage and add more turns (or part turns more like) to ALL the spokes evenly.

Next we do the same thing but from one side of the wheel to the other. So grab a crossing and the nearest one on the other side and, you guessed it, squeeze like crazy again. Go round at least twice but the more the better.

This month’s tech column is going to be about chain tension. But before I get on to that I should probably ramble on about something pretty much unrelated for a while. In this case I want to get you to take a minute to think just how awesome bicycles are. I was awestruck the other day watching the aftermath of the London tube and bus bombs. People were talking about their fear of getting back on the underground but saying they had no option… No option!?!? It’s the middle of summer the tube network only extends about 8 miles from the centre of London anyway and London is virtually flat. Why not get on a damn bike?! Do you know what the statistics for terrorists bombings of bicycles are? I had dreams of seeing the roads of London suddenly full of cyclists cruising down the empty bus lanes, saving their tube-fare and getting some much needed exercise… Sadly it never happened. But remember that that bike of yours can do more than just tricks.

Anyway back to chain tension. We have all experienced the dilemma pretty much every time you take off your back wheel and come to put it back on. Sure you can run a Halfords/Fly Cobra inner-tube, but sooner or later you will need to take your rear wheel off, and when you do you will have to set the position of your back wheel just right to get the chain tension you want. You will also need to be thinking about getting your tyre central in the stays of course. After some wrestling you get it set and then you have to check it by cranking the pedals round a few times, because the chain tension varies! Why is that? Why do we have to adjust and re-adjust the wheel position so that the “tight-spot” isn’t too tight and the “loose-spot” isn’t too loose? Why is there even a tight and loose spot in the first place?

This is going pretty badly isn’t it? Can you tell that we are rapidly approaching deadline and I am struggling to write anything worth reading here… Time to play the “old school” card…

If you just force the cups in then the pressures can be quite incredible. The cartridge bearing can get significantly compressed by these pressures and may not spin as well as it should.

Un-even chain tension is usually down to one of 3 things. Your front sprocket isn’t quite central. Your rear sprocket isn’t quite central. Your chain is stretched unevenly.

In the first case; if your sprocket is loose on the BB axle then it will inevitably move off centre. This means that the sprocket moves backwards and forwards as you pedal, which has the same effect as constantly moving your back wheel about in the dropouts. The second cause isn’t nearly as bad as it used to be. Cassette hubs are usually pretty well machined and sealed bearing hubs and modern freewheels also tend to spin much more centrally than old loose ball hubs which had a tendency to be machined off centre.

Chain wear or stretch is the most neglected cause. Believe it or not chains “stretch” over time, the pivots wear and become loose and tricks like disasters only make it worse. So instead of ten, half-inch long links adding up to five inches they might be five point one inches long, and to complicate matters the next ten might not be stretched as much. As these different length links move round the drive train they can be pulled to the right length as they run over the sprocket teeth (or allowed to sink deeper on worn teeth) and this makes the chain length (and therefore tension) vary.

First get the bike upside down and stable. You can check the chain tension by wiggling the chain up and down but if the tension is set up OK you should just be able to feel the extra resistance as you move the pedals. Now move the cranks to the position where the chain is tightest. Remember where it is. In my case it is with the right pedal at the top (or bottom when the bike is upside down). Next give the cranks several turns and check again. Is it still in the same position? Do it a couple more times to double check.

If the tight spot is always in the same place (eg. the chain is tight every time the right pedal gets to the top of it’s stroke and it happens every turn, and the loose spot is opposite) then the problem is with your front sprocket. If on the other hand it changes every few pedals; so one minute it might be with pedals up and down and next it is when they are level, then there is a problem with the chain or rear sprocket.

Of course very often there is a problem with more than one part of the drive-train. If you have done some hard “rocks” then you might have stretched the chain un-evenly, but it is also very likely that you have mashed in a few sprocket teeth and moved the sprocket off centre too. In this case you will need to spend a little time figuring it out, maybe there are two tight spots sometimes, maybe the tight spot is uber tight on one occasion and not as bad on the next rotation.

So now you know roughly what is responsible for the problem, but what can be done to “fix” it?

Well first off you need to be realistic about how good it can ever be. Pathetic as it may seem, it is pretty much impossible to get perfectly even chain tension. You are always going to have a bit of a tight spot so if you were hoping to get rid of it entirely then forget it. Having said that, if your chain makes a horrible “crunking” noise as you go through the tight spot, and/or almost falls off in the loose place then you do need to try to improve matters.

If your tight spot moves around then look to your chain first. A broken chain is such a nasty failure that it is generally worth spending a tenner on a new one if you are at all worried about your current one. The rear sprocket is the other possible cause but it is only likely to be a serious problem if you run a free-coaster. Freecoaster drivers can become distorted and this leads to all kinds of weirdness.

But the most likely scenario is that your tight spot will be consistent with crank position and the front sprocket will be to blame, so look at it. If your teeth are mangled to hell on one side or it is obviously bent then it may be time for a new one. On the other hand it is surprising how many people simply install it wrong. Before you take it apart it is worth making a few marks on it to remind you where the chain was in contact with it when the tight spot occurred. Most sprockets need a “top hat” spacer to fit between the sprocket and the crank axle. This should nearly always be fitted with the ÒbrimÓ of the top-hat on the bottom bracket side of the sprocket rather than the crank arm side and it MUST be the right size. It should be a good tight fit into the sprocket and nice and snug on the axle. If it visible wobbles on either of these then either get a new one or try to shim it out with some baked bean tin. Many people use a pop can to make a shim but this soft aluminium isn’t nearly as effective as the steel of a baked bean tin. The shim should be even all the way round the spacer but if this isn’t possible then you need to put it at the back at the point when you normally get the tight spot. In other words, if the tight spot occurs when your right pedal is at the top (as mine does), then the sprocket is obviously at its furthest forward point when this happens, so shimming the opposite side to the part the chain is on will help bring it back to the centre.

People like Jeremy Clarkson often talk about torque. Unfortunately they either just quote a number or skirt right past it like it is this incredibly difficult concept to understand. The truth is that torque is very simple to understand. Time for another dumb simile… (hard to believe that that is really how you spell simile but I cant think of anything better so lets go with it)

Suppose you go down to the playground with your pet elephant and want to play on the see-saw together (happens all the time I know). Well, as long as you go to the elephant-specific playground you can stick “Trumpy” on one end of the see-saw which immediately puts the other end right up at the top. So you climb up on your side and nothing happens. Sure you can get Trumpy to kick off from the ground to get things going, but he will just drop down again super fast and bruise his bum while you get hefted into the air again. No fun for Trumpy. Being a rainy day there are no other people in the park for you to get on your end, so you shout to Trumpy to move up towards the pivot more. As Trumpy moves nearer the middle of the see-saw things improve, until finally you reach a point of balance. Now you can see-saw gently up and down to your hearts content before heading home for tea and buns…

THAT is torque.

A shorter, less elephant-based way to describe it, would be “turn-y force”.

More technically it is, force times distance (from the pivot). So if Trumpy’s weight applies a force of 10,000 Newtons (1000kgs-ish, quite svelte for an elephant) 1 metre from the pivot (centre) of the see-saw then he applies a torque of 10,000 Newton meters. So assuming you apply a force of 1000Newtons (you weigh 100kgs?!? you fat bastard!!!) then to apply a balancing torque of 10,000Nm you need to be 10 metres from the pivot (thank god for elephant-specific playgrounds). This is called “mechanical advantage”.

In BMX we are more usually talking about tightening bolts and nuts. We use a spanner or an Allen key and put a force on the end to turn it. From the above bollocks, we can see that we have a choice between putting a huge force on a short spanner or a much smaller force on a longer spanner. If your spanner is twice as long you only need half the force on the end to achieve the same torque.

However what most BMXers have a tendency to do, is use an extension bar to double or triple the mechanical advantage AND heave all their strength on the end.

Nothing is infinitely strong. Everything has its limit. If you apply a big enough torque to any nut or bolt, then eventually something has to give. The bolt might snap, stretch or rip the thread out of it’s hole. The head might round off or out. Or the component it is fixed to might crack or bend.

It is therefore pretty important to have at least a rough idea of how tight we should do up the various nuts and bolts on our bikes.

Ideally we would all rush out to buy torque wrenches, and manufacturers would mark every nut and bolt with the correct tightening torque for optimum performance. A torque wrench lets you pre-select a torque and when that torque is reached then it makes a little click noise and you know to stop; so with each bolt you would look up it’s torque rating in the instructions, then set your torque wrench and bob’s your uncle, perfect.

Realistically this isn’t going to happen is it? But even if it did there would still be problems. Because we donÕt actually care about the tightening torque do we?

Hang on George what are you on about? I just read all this crap up to here and now you are telling me it’s irrelevant? Sheffield’s not too far for me to come up and smack you you know!

OK just give me a minute, and with luck you will see what I am getting at.

What we actually care about is the tension in the bolt. The bolt’s job is to hold two (or more) parts together, and this is down to how much force it is pulling together with. Now with a perfectly lubricated and machined bolt, in a perfectly lubricated and machined hole there IS a direct correlation between the tightening torque and this tension, but who has a perfectly lubricated bike?

So if you try to tighten your badly lubricated brake-boss-bolt into your slightly rusty old frame, with your brand new torque wrench set to the perfect pre-set torque, then chances are it wont be tight enough. Lots of your torque will be lost overcoming the rough-ness of the thread.

This is why you have to use your judgement. So after all this mumbo-jumbo (emphasis on the jumbo Waddy, emphasis on the jumbo) what I am telling you to do is make a guess. If a bolt feels stiff then it is likely to need a little more torque than if it feels smooth.

Either way the chances are that right now you have a tendency to over do it. A lot. MOST people do MOST bolts up WAYYY too tight. Do up a brake-boss bolt and it should only need the slightest of nips to stop the springs slipping, keep adding pressure and you are very likely to distort the brake boss on the frame, this leads to binding brakes and a lot of headaches. The only solutions to this once it happens, are to really know what you are doing and tickle the boss back to shape or to get a new frame. So for f***’s sake go easy on them. Do you round out the heads of the allen bolts on your stem? Chances are you are overtightening (or using the wrong size allen key, or both). Stems are tricky buggers. What works perfectly for one rider can seem like junk to another and the difference is very subtle. Stems absolutely rely on being clean and having good knurling on the bars to work well. When holding a pair of bars we have a huge mechanical advantage over the stem so good grip is essential. The coefficient of friction between the bars and the stem is much much more important to the overall situation than how tight you do the bolts. More than a tiny waft of paint on the knurling will spoil the grip immesurably so burn or scrape it off if you can. It is vital that you grease the stem bolts but you really don’t want to get any of this grease onto the bars or the clamp area of the stem. Once a stem has slipped once, don’t just try to re-tighten it more. That knurling slipping inside the stem will have shaved off fine bits of aluminium that can act like ball bearings, if there is grease in there too then no amount of tightening will get it to grip very well. So take it all apart and clean everything up. The same goes for the other end of the stem. Grease is vital to the smooth working of your headset but you really don’t want ANY on the steerer-tube or the stem at the point where they meet. Having said all this, you still need to tighten most stems down pretty tight, but if you are having to resort to an old seatpost on the end of the allen-key then something is fundamentally wrong…

Some things DO need to be very tight and these are usually obvious because they use a hexagonal head or flats so you can get a proper spanner on, instead of a poxy little allen-key. Wheel nuts and pedals are two good examples. Clicking from cranks is often due to insufficiently tightened pedals, just make sure you lubricate the threads well so that your precious torque goes into useful tension. Wheel nuts can be a pig. Ideally we want them super tight to prevent the wheel slipping in the dropouts, but the difference between nice and tight, and a bunch of stripped threads, can be a very fine line. Again, keeping the grease and crap off the dropout will help prevent wheel slippage but generally this is just something you need to get used to.

Probably the most important, and most overlooked are spokes. There are probably between 72 and 96 of these on your bike, and while it may seem like a ball-ache, you really NEED them all to be nice and tight all the time. To judge the tension, grab a bunch of spokes and squeeze them in your hand. As the spokes start to dig into your hand painfully they should only have moved a couple of millimetres each. If they move more than this then go read the old tech column on wheel truing and get busy, it isn’t rocket science and it will make a huge difference to the feel and the life-span of your wheels.

When the very first bicycles were being developed, simplicity was king. We are talking about Scotsmen scooting about on wooden frames with wooden wheels and wooden forks. This soon developed into the first real bicycles, where rather than pushing along with your feet on the ground cranks were fitted directly to the wheel of the “ordinary” (or penny farthing)

Not happy with the slightest bump causing them to fly over the bars onto their face from 10 feet up, designers searched for a way to make a “safety” bicycle. The key to this was the invention of the roller chain, which allowed the cranks to be moved off the wheel itself and therefore the rider too.

Since then a lot of lycra-clad, leg-shaving freaks have tinkered around with the chain quite a bit to get gears but essentially we are riding much the same technology today.

For some reason a lot of BMXers have problems with their chain. Some would say that it’s the way we smash it against things. But even if you look after your chain and refrain from mashing it into every wall you come across, it can still let you down badly.

Chains have a great sense of humour. What they will do is wait patiently for you to really crank hard at something, then they will suddenly snap and watch as you throw yourself into the front wheel of the bike. Ideally this should be in a crowded area or busy main road. So this month let’s look at the chain.

ALL bicycle chains are made up of inner and outer plates. OK so not all chains, the Shadow interlock chain is slightly different in that it is made up of “cranked” links but just ignore that for a minute and I am sure you will be able to work out the differences for yourself.

Two Inner plates are typically fixed together in a pair by two little hollow cylinders (though often these cylinders are formed by squidging the middle of the link inwards so it is one piece). These cylinders are a tight fit in the side plates so that this little assembly holds itself together. Around the outside of these hollow cylinders run rollers. Basically just another slightly larger hollow cylinder that is free to spin on the first.

Outer plates are also fixed together in pairs but by a thinner solid pin than the inner link. Again this pin is a tight fit in the plates to hold it all together.

But these pins are slid through the hollow pins of the inner links to link all the links together.

 

As long as there are gaps for all these things to move freely then everything should be peachy.

Yes. This IS all very obvious if you look at it but have you ever really bothered? You have? Oh. Sorry…

Anyway, once you think about it this way, it is easy to understand the common problems.

One of the most common is the “stiff link”. If you crank the chain round some of the links may not pull straight on the bottom straight run of chain. This is caused by the outer links being pinned too tightly around the inner.

The key to fixing or preventing this is knowing how to use a chain breaker correctly. When putting a chain together there are two sets of baffles to support the chain. When you put the chain in the furthest over position then you push the pin against the far plate. This helps it get started without simply shoving the plate out of the way. But once the pin is nearly all the way back in it will be making the link bind up. To stop this you then move the chain to the nearer position to the handle, and add that last quarter turn or so. These nearer baffles support the nearside plates so that as the pin moves that last bit it takes the far plate with it, thus opening the width slightly and making the room for the chain to flex cleanly.

Assuming you can get your chain together cleanly without pushing the pin too far over or making a stiff link then the biggest problem is getting a good “chain-line”.

The chain really needs to run straight back along the bike. The sprocket and freewheel are both aligned exactly parallel to the frame but if they aren’t offset from the centre line the same amount then the chain will have to bend sideways as it comes off the sprockets. If there is any significant bend then, only the sideplates on the outside of the bend can transmit the force. This can effectively double the load on the chain and greatly increases the chances of it breaking. This misalignment also makes the chain try to work itself apart as you pedal which doesn’t help.

Most people just eye this up to check the line, but with the chainstay snaking through your field of vision and the bulk of the tyre on one side this technique isnt very reliable. Mush better is simply to measure everything.

Your whole bike should be symetrical so if you measure the width of your hub, divide by two and subtract the distance the sprocket is from the dropout. Then this dimension is how far your chain should be from the frame centre-line.

 

If you next measure the bottom bracket shell width, divide by two, and add the distance to the front sprocket then this SHOULD be the same.

Remember to measure to the centre-line of the teeth for consistency.

The numbers above are just EXAMPLES, you dont have to have these exact numbers.

In this case you can see that at the back we have:-

108/2 = 54
54 – 15 = 39

Then at the front we have:-

66/2 = 33
33 + 6 = 39

So everything is as it should be.

Obviously if your frame is bent then these numbers are pretty meaningless but you can look at tech column 83 to help you check for that.

One of the least common questions about chains is how often should you lubricate it and what with? It is quite reassuring that this question isn’t that common, because for BMX, lubing the chain is pretty unimportant. Most chains will come nicely pre-oiled, all you need to do is bung them on and go ride. Adding extra oil is all very well if you are a road racer riding hundreds of miles but for bums like us it really isn’t that important.

Having said that, if you ride in the rain or wet quite a lot then the oil inside the chain will slowly wash out and leave your chain dry and inefficient. Ideally we only want lube between the central solid pins and the hollow pins (or bushes), and between the bushes and the rollers. Getting it there, is down to either soaking the chain or dripping a drop of lube on each roller independently. Either way you then need to really clean off the outside of the chain to stop the excess lube attracting all the dust and crap from miles around and gluing it to your drive train.

 

 

Chances are that at some point some incredibly witty sort will have shouted this tired old phrase after you as you roll down the street. You may have noticed that they wait until you are a fair distance away before they shout it, and they don’t hang around to hear your equally witty rejoinder of a punch in the bollocks.

But what if they were right?

Maybe a change from a 20.5inch to a 20.75inch top tube would make all the difference? Maybe that pain in your lower-back would subside? Maybe you would be able to twist the big double without looping out so much? Then again, maybe your manuals would go to shit and you wouldn’t be able to get back to the pedals on tailwhips anymore?

So let’s look at frame sizing in this month’s exciting tech column.

OK, you know the drill, put the kettle on and maybe hunt out some biscuits. Don’t worry I am not going to crowbar in another rubbish analogy I just think you will enjoy this more with a cup of tea and a biscuit… OK maybe that’s expecting a bit much, but maybe you will at least enjoy the tea and biscuit, and think fondly of the article for suggesting it.

So first off, how are frames measured? The short answer is; stupidly.

A tradition has developed of frame makers quoting the top-tube length, but it’s a pretty vague way to measure a frame. Top-tube length is measured along the centre-line of the top-tube from the centre-line of the seat-tube to the centre-line of the head-tube. This is a useful dimension to know if you are building a frame, since this is the length of tube you need to cut for it. But for comparing one frame to another it is unreliable.

Imagine two frames. Both quoted as having a 20.5” top-tube and a 74.5 degree head-angle. But one has a 72 degree seat-tube angle and the other has a 71 degree seat angle. ‘One measly degree’, how much difference could it make?

Well quite a bit. Assuming an 8.5 inch seat-tube length (centre of bottom bracket to centre of top-tube) then one-measly-degree is equivalent to 0.15 inches. Just 1.5 degrees steeper seat-angle would make a 20.5 inch top-tube feel like a 20.75…. Which is really noticeable. Add in variations due to the height of the top tube, and head-angle etc, and things only get more vague.

But there is a lot more to frame size than just top tube length.

I covered head-angles and their effect on steering feel a few months back so I am not going to go over the same ground, but head-angle also has an effect on the feel of the overall length of a bike. To understand why we need to consider the basics.

What matters to us as riders is how the bike feels.

As you ride, your primary concern is with where you meet the bike, and where the bike meets the ground. Your ‘points of contact’. Where your feet are, where your hands are and where the bike touches the ground.

Where your feet are is down to a whole raft of variables. From how long your cranks are, right down to how thick your pedals are. In terms of factors the frame determines, then bottom bracket height is the obvious one. Since most of your weight rests on your pedals and so on the bottom bracket, it determines how high above the ground you are. But also, as Einstein pointed out, “it’s all relative init.”

So the position of your feet RELATIVE to the position of your hands and RELATIVE to where the bike meets the ground. These are the key things.

Long low things tend to be more stable than short tall things. If your bike has a long wheel-base then just like a stretch-limo’ it is harder and slower to turn, but stable at speed. As the wheel-base decreases it gets more like a Smart car and will turn on a sixpence but the trade off is that at high speed it is much less stable.

Now admittedly with bike frames we aren’t looking at variations anything like this big, but most people will really notice a quarter inch change in top-tube length.

So wheel-base length is important but this isn’t the same as top tube length is it?

Imagine a frame with a 71 degree seat angle 20.5inch top-tube and 75degree head angle; you might think that this would be very similar to a 20.5inch top tube frame with a 72 degree seat and 74.5 degree head angle? BUT you would really feel the difference between the two. The front end of the second frame would be longer by 0.15inches because of the seat angle and another 0.15inches longer because of the shallower head angle, giving a total change of well over a quarter inch.

So remember a degree steeper on the seat tube will mean a frame’s front end is effectively 0.15” longer and a half degree steeper head angle will make a frame’s front end effectively 0.15” shorter.

So what about chain-stay length?

Well this is a much more sensible and useful dimension to quote. Chain-stay length obviously contributes to the total wheel-base, so a longer chain-stay will contribute towards a more stable bike that is harder to turn. But chain-stay length also determines how hard the front end of the bike is to get up and how stable it is once it is up there.

Try this little trick; put your tea down for a minute and go find a broom. Right, now lift the broom up vertically and stick the end on your nose, OK adjust it until it is dead vertical then take your hands away and move your head about to keep it balanced on your nose…. You should be able to do a few seconds at least.

Right, now get a tea-spoon. Do the same trick, stand the tea-spoon vertically on the tip of your nose, take your hands away and move your head about to keep it balanced. I’ll bet you a fiver you cant balance it for more than 5 seconds. (send cheques made out to ‘George French’ to the magazine).

The point of this little demonstration is to show that contrary to what you might expect it is easier to balance high above something than it is when you are low down to the pivot. This is the time constant. It’s a lot like a pendulum turned upside down, a long pendulum takes longer to swing than a short one so you have more time to correct.

So although short chain-stays make it easier to pull up into a manual, they make it harder to balance once you are there. It’s a slight effect and it really shouldn’t make the difference between being able to manual and not but it does play it’s part in the overall feel of the bike. This length is also a crucial factor in how fast the bike turns. Since most of your weight is centred over the bottom bracket, this time constant applies to turns as well as manuals.

Over the years we have seen tiny changes in these dimensions but with an obvious trend. Front ends have got longer with steeper head angles, while back-ends (chain-stays) have got shorter. This has kept the bike fairly stable but helped make for a bike that turns quicker too.

Stem length. There is a common misconception that a longer stem will help make up for a short top-tube. This is pretty much bollocks. Simply moving your bars forward will have an almost identical effect to running a longer stem except of course that the “style police” will shoot to kill if they catch you with your bars set steeper than your head angle.

Moving your bars forward (or using a longer stem) will give you more room up front but it wont make the frame feel any longer, it will still spin at the same speed and have similar stability. The only real change will come with front wheel tricks. Putting your weight further forward it will make a significant difference to the feel of front wheel tricks.

So next time you look at buying a new frame don’t just look at the top-tube length and assume that one 20.5 inch top tube frame will be much the same as another. Think hard about your current frame. Do you loop out on high speed 360s? If so maybe you could do with something a touch longer? Maybe you feel that the frame is damn slow to come round on tailwhips? If so a shorter bike will spin that much quicker (it doesn’t matter that you aren’t on it the rules are the same).

But above all else, remember that the bike needs to fit you and feel comfortable, taller people tend to need longer bikes and shorter people shorter ones but if you are happy on your bike then don’t change just because you think you should. Try your mates bikes to see how they feel and keep in mind that a quarter inch change in top tube length is quite a lot.

When the ancient Egyptians were laying out the great pyramid at Giza over four and a half thousand years ago they had little more than bits of wood and string to help them lay it out. And yet they got all four sides bang on the four compass points and the lengths of the sides accurate to better than 0.1%. Time has taken its toll on the outer skin but it is still dead square and straight…

However in all that time they never once tried to 360 a set of stairs on it either…

Over my years of riding I have seen a lot of very talented riders do truly amazing things on bikes that were basically fucked. I have seen The Punisher manual a frame that I know to be severely bent for mile upon mile with no more evidence of a struggle than a little more pumping than usual.

Unfortunately we cant all be this gifted, and for the rest of us a twisted or bent frame can hold us back for as long as we own it. My own struggle with a bent frame resulted in not being able to manual in a straight line and turning the opposite direction for months after I finally replaced it with a straight one.

So the purpose of this months technical column is to show how you can check your frame for the less obvious damage like twisting and bending that might be at least partially responsible for your erratic riding style…

Most frame distortion takes place in the rear triangle of the frame. It is obviously much much easier to bend a three quarter inch chainstay tube than an inch and a half down tube. Although the tendency to stronger bigger rear axles has helped to brace the two sides of the rear triangle against each other they are still the weak point of any frame. Tricks like tailwhips and any twisting trick inevitably lead to the odd bodged landing. When you come down travelling any direction other than straight forward, or when the back end smashes sideways into the ground, then inevitably the side loads to the rear wheel get transmitted into the back end of your frame.

There are two main ways that your back-end can distort; bend and twist.

Checking for twist;

Checking for twist is pretty simple but requires a good eye. Simply sight along the frame from the headtube and look to see if the back wheel is in line with the seat tube. Ideally you should see the headtube, seattube and rear tyre all nicely lined up, indicating that everything is OK. Obviously this requires you to have a reasonably true wheel to check against.

Checking for bend;

Bends are generally worse than a slight twist, not only do they throw your balance off but the chainline can be effected and in extreme cases the crank arm will start to hit the chainstay.

You can check for a bend easily enough with a piece of string and a ruler. Simply tie a piece of string to one dropout, loop it forward round the headtube and back to the other dropout. At the point where the string passes the seat-tube take a measurement (with the ruler) from the seat-tube to the string. It should be the same on both sides of the frame. Any inconsistency should be about the same as the amount the back end is bent. So if the string is 2mm nearer the seat tube on one side than the other then the dropouts are about 2mm off line.

A couple of millimetres isn’t a big deal but I have seen plenty of frames where it was well over 10mm, which was enough to make the frame FEEL very bent.

Other frame damage;

While you are inspecting your frame it is a good idea to look for cracks and ripples, any early warning of impending failure could be the difference between a summer spent riding a new frame or a summer at the dentists using that money to buy new teeth… Look all round every weld for signs of cracks on the weld or within a few millimetres in the “heat affected zone”. Ripples occasionally form in the top or down tubes as a result of head on crashes and soon get worse. It’s like the trick where you stand on a coke can and the slightest tap causes it to collapse.

Forks;

Forks nearly bend on the steerer tube before the legs bend, this means that the bend itself is inside the headtube of the frame where you cant easily inspect it for damage. However there is a tell-tale indicator. If the steerer tube of the fork bends then it nearly always bends just a little above the bottom headset race, so forcing the headset apart slightly. By looking closely at the bottom headset cup it is fairly easy to see instantly any problem with the fork steerer tube. If the bottom part of the headset (the cone that you hammer on to the forks) is perfectly parallel to the bottom of the cup itself then things are almost certainly fine. BUT if there is ANY misalignment visible then it’s a pretty sure bet that the fork steerer IS bent.

Forks can also bend sideways and/or twist. The way to check for these is simply to have a really good look at them, squint down from the top, check the headset again but from the front this time.

Forks are one of the most vulnerable and critical parts of your bike, people who snap their forks clean off usually hit the ground a lot harder and a lot faster than they like, so don’t take chances with them. Check the welds for signs of cracking too.

Bars;

Bars usually bend down at the grip section, often just next to the lever or by the weld for the cross bar, but they can also bend down by the clamp bar or twist. If the bars are on the bike then just look down at them to see if the cross bar and clamp tube line up with each other, if they don’t then the bars are twisted. To check for bends then simply turn the bars sideways and measure from the tip of the seat to the end of the bar, then turn them the other way and compare it with the dimension on that side. Bear in mind that if you have mounted them on the piss or made an arse of cutting them down then that could distort the measurement too. If the bars are off the bike then just lay them on a table and test for “rock” to determine if they are twisted.

—————————————————————————-
More Bottom Bracket News:

Another month has passed so as you would expect ANOTHER new BB size has been introduced. This one is slightly special though since it is from Profile.

Profile have long been a dominant force in the 3 piece crank market but less well known is that they also make frames. I don’t know how many they sell, I cant remember ever seeing anyone riding one down my local park, but with their influence on the crank market anything they do is going to be closely watched by the industry.

The Mulville frame uses a bottom bracket that Profile call a “Hybrid” bottom bracket.

Like many of the new bottom bracket sizes it uses no cups with a standard cartridge bearing pressing straight into the shell. Unlike any of the other designs in use this bearing does not accept the crank axle directly. Instead there is a system of spacers to shim the various axle sizes up to the one-size-fits-all bearing. Details are still hazy at this point so this is just conjecture but it seems likely that this is done so that the system can use cheap readily available off-the-shelf bearings.

At first glance this may seem to be a really good idea. It should (hopefully) be able to accept all existing crank sizes with a single common bearing. The size they have chosen looks fairly large (somewhere between a normal USA BB bearing and the “Spanish” bottom bracket bearing) so it should be reasonably strong and long lasting and the shell looks fairly light and tidy.

BUT, there are factors to consider that may cause big problems.

With the normal arrangement of the crank axle fitting straight into the bearing and a cup on the outside, then if the bearing is a poor fit in the cup the tension in the chain always acts in the same direction relative to the bearing. So for example if the bearing is loose in the cup then it will be pulled to the back by the chain tension and down by your weight on the cranks, then it will stay there.

However if there is a slight gap between the crank axle and spacer, and/or a gap between the spacer and the bearing; then, because everything is constantly rotating they will be forced to “roll” around inside each other.

This isn’t a new problem to BMX’ers. If you have ever had a poor fitting spacer between your sprocket and crank axle then chances are you will have noticed it slowly get looser and looser and the chain tension get more and more un-even.

So the question-mark over this new “hybrid” bottom bracket has to be, “will Profile be able to get the spacers just right?” My guess is that it will be almost impossible to make these spacers cope with all the slight inconsistencies in crank axle sizes well enough to avoid nasty creaking noises and excessive wear. Then again, as the dominant crank maker, if anyone can keep these tolerances between crank and bottom bracket under control it will be Profile….

Lets also hope they chose a good bearing….

Click click click. Or if you are running certain cassette hubs; CLICK CLICK BASTARD CLICK CLICK CLICK, or even CKCKCKCKCKCKCKCKCK.

Some people seem to like a really loud click when they freewheel, some people hate it.

Personally I hate it, it’s the ultimate give-away to security guards and police. If you need to sneak about to get to a street spot then having some fucker’s cassette hub making super loud clicks that can be heard two streets away is kind of a bummer. On the other hand I really can understand how some riders find it a useful indication of their speed. “Click… click… click…”; too slow. “CKCKCKCKCK” too fast. “Clk, clk, clk,”; just right… But is there anything you can do about it either way?

Yes.

The click you hear is each pawl of the cassette or freewheel as it springs out after each tooth has passed and it smacks into the trough between teeth. If you fill the mechanism with thick grease then it will “damp” this movement and cushion the impact of the pawl against the toothed part of the hub. So adding thick grease will quieten the hub substantially. Unfortunately if you over-do this then the pawl might not make it all the way back to position between each tooth and it might slip under load. Far from ideal.

If on the other hand, you clean out what grease there is in there, and replace it with just a very thin smear of thin oil, then there will be almost no resistance for the pawl and it will make the loudest click possible (and be less likely to skip or slip).

Between these two extremes there are an infinite number of options, different thicknesses of grease and oil will give varying degrees of damping and therefore sound level.

With cassettes and freewheels that use individual springs under each pawl, you can also bend these springs out a little to give more spring and so more noise (or less chance of slipping with a thicker quieter grease).

At this point it is useful to know that you can “thin” grease by mixing in more oil (grease is traditionally just an emulsion of oil and water with ‘soap’). Take your normal grease and mix in some WD40 or other thin oil and it will become thinner and less viscous.

While we are on the general subject, it is worth mentioning that all freewheels and cassette hubs need a little love now and again. If your freewheel or cassette hub is slipping or making nasty noises then it will need a bit of attention.

With freewheels, taking them apart IS an option but its not much fun so make it the last resort. Instead, just dripping some thin oil in through the crack between the toothed part and the “body” is often all it needs. And by “dripping some” I do of course mean “pissing a shed load”. With freewheels this oil needs to do the job of both cleaning and lubing so you need enough to wash any “crap” out the back. Keep spinning the freewheel to work it through and you should notice a dramatic improvement.

With cassette hubs you MUST take them apart to clean and re-lube them. Getting thin oil like WD40 into the wheel or driver bearings is a death sentence (this applies to freewheel hubs too so keep it away from the hub bearings).

Most cassettes are fairly easy to take apart but those pawls and springs can and will make a bid for freedom so keep an eye on them and be ready to catch them.

With all cassette hubs you will need to undo the cones from at least one side and completely remove them to get the driver off. Once you have done this simply pull the driver gently out of the hub. With some hubs the axle will remain in the hub and with others it will come out with the driver (this type, like the newer Odyssey cassettes, will need the non-drive side’s cone nuts removing to allow the axle to come out). If in doubt just remove BOTH sides.

Once you have the driver out, wipe out the insides with an old rag and then apply your chosen lubricant. A light smear of thin oil (like brake-cable lube) for those who like the noise; a small amount of thin grease for the stealthier rider; and a carefully judged thicker grease for those who need to be as quiet as possible.

While you have the hub apart take the opportunity to inspect everything especially the axle. Spin the axle slowly in the hub and look for “wobble”. Or roll it along a flat surface. If it wobbles or looks bent then replace it straight away.

Remember that the bearings are locked to the axle by the cone nuts, so if the axle is out of line at the bearing seats, then the bearings are no longer lined up with each other. So as the wheel rotates the bearings try to angle inside the hubshell on every turn to line up with the axle. This soon leads to them wearing out the bearing seats in the hub shell and that is that for the hub. Repair is next to impossible and your only realistic option is a new hub.

On the same subject; have you ever noticed how cassettes and freewheels are often advertised as having many more pawls or teeth for; “faster engagement” ? Who asked for this? Why is it a GOOD thing?

The truth is that faster engagement can be a real pain in the arse… literally.

A few years ago, as an experiment, I made a prototype hub that used a ‘one way roller bearing’. One way roller bearings are a type of very expensive needle roller bearing where each roller sits on a little ramp held against it and the outer shell by a tiny spring. In one direction it sort of rolls and in the other it jams up INSTANTLY. The hub has literally “zero slack”. It felt amazing.

Going forward it made no clicks, was absolutely silent and smooth as hell.

Going backward, even a little bit, it just threw you off the bike.

It may seem hard to believe, but with an ordinary freewheel or cassette hub you get a fraction of a second to absorb any backward landing, before it asks you to back-pedal.

With the roller hub the very moment that the back tyre touches down it forces the front pedal up at you super hard. But at the moment of landing you also have to be coping with the forces of your landing.

In other words, with a normal set-up you land, on both pedals and then start pedaling back. With the roller hub you land on two pedals where the front pedal is coming up at you twice as hard as the back pedal which is trying to retreat from under your foot. The result of all this is that it blows you straight off the bike and onto your arse…

The experience of the roller-bearing hub taught me that some slack in the drive-train is essential, so why are companies bragging about having reduced it nearly to zero?!?!

Obviously too much slack can be a pain too but there is definitely a “right amount”. Don’t be impressed by claims of near instant or instant engagement; at the starting gate it may be a help, but on street it’s totally counter-productive.

Bottom Bracket News Continued…… again

Well you cant honestly say you are surprised can you? That’s right its time for another instalment of bottom bracket news….

But this month it is at least partially good news.

Since the last article on the continuing bottom bracket saga, FBM have gone ahead and launched their “Mid Size” bottom bracket. If you can remember from 3 issues ago, the FBM Mid Size uses the standard bearings that come stock with Profile and other ¾” (19mm) axled-cranks. They press straight into the frame and offer bearings with a proven track record for strength, but in an easy to fit styley. The downside is that other sizes of crank like (22mm) Powerbites, just wont work with it.

Well now that may be about to change. Haro/Premium have taken quite a liking to the Mid Size (after apparently having some problems with breaking Spanish Bottom Bracket bearings) and are talking seriously about making a custom bearing to allow the Mid Size to accept 22mm axled cranks… This still leaves little room for future development on new crank axle sizes though…

Also a new(ish) development since the last article on this subject:-

The Sputnik frame uses normal euro bottom bracket bearings but in a press fit shell rather than the traditional threaded euro. On the rumour mill Profile are said to be working on their own bottom bracket standard, and S+M still haven’t declared what they are going to do.

From left to right: Unthreaded Sputnic ‘Euro’, Traditional Euro, Spanish BB, Mid Size, USA

“Supertherm or Ox platinum? T45 or Reynolds 853? Sanko or Tange? What’s it all about?”

Yep, several people have been foolish enough to ask me to write a tech column on all the “fancy” tubes that companies are increasingly using to make frames. Obviously this is unlikely to be an exciting story with dumb security guards and drunken antics but I will do my best to prevent it being completely unreadable.

First job though, go and put the kettle on. You will need it later and you don’t want to have to wait for it to boil. From here to the bit you need the kettle for should be just about right to let it boil, only boil as much water as you will need for a cup of tea. If everyone only ever boiled enough water for the job we could close two power-stations….

OK lets go.

Most of us are familiar with 4130, we look for a frame that is made of “100% 4130” as a minimum. But what is 4130?

4130 (and all this other fancy new tube) is over 95% Iron. Iron is a metallic element (Fe), you can’t break it down any further without getting into nuclear physics type stuff. Stick it on the hob as long as you want, it wont separate or curdle, hit it with a big stick, call it names, it wont have any effect. Iron is iron is iron!

But iron on its own is what “we in the trade” like to call “piss weak”, sorry to get so technical but its unavoidable. Raw elemental iron is about a tenth the strength of 4130. But 4130 is 95% iron! Obviously those other few percent of something-else are pretty damn important.

Do you remember in chemistry at school all that stuff about reactions and compounds? Drip some hydrochloric acid onto some marble chips and write down all the reactions taking place? Yeah well that has ABSOLUTELY NO RELEVANCE TO THIS so don’t let it distract you.

Kettle should be about to boil so go and make a cup of tea.

Back? OK.

What you have in front of you is my makeshift analogy for this month. When you made the tea it didn’t fizz and bubble with chemical reactions did it? (it shouldn’t have anyway) no gas was emitted and it didn’t glow like in the movies? That’s because it is simply a mixture. You dunked the teabag and small particles of tea leaf moved out of the bag into the tea they are just floating about in there. The same with the milk, you watched it swirl round and mix in with the water and tea-leaf-bits. Even the sugar (if you take it) although dissolved is not chemically bonded to anything it has just collapsed into tiny tiny bits that are floating about in there. It’s still 99% water but it tastes immeasurably better. This is the same as our 4130. Other metals like chromium and molybdenum as well as other elements are mixed in with the iron but they aren’t chemically bonded together.

You can drink the tea now.

Metals are crystaline. So the iron in our tube is composed of tiny little crystals all jammed together. The bonds within these crystals are immensely strong, but the bonds from one crystal to the next are relatively weak. So stick a bit of iron in a vice and hit it with a hammer and it will bend fairly easily because the crystals can just pull apart.

Steel is iron with a little carbon mixed in with it. The carbon gets in the gaps between the crystals of iron and glues then together. Now if you hit a lump of Steel rather than iron you will have a much much harder job to damage it. Remember nothing is chemically bonded together, the carbon has NOT formed any molecular bonds with the iron.

Man has been making steel a long time now and we have got very good at it, tiny differences in the amount of carbon can make big differences to the strength of the steel, but we have taken simple carbon steel about as far as it will go.

To get more out of the Steel we add other metals. Just a little bit, one or two percent, takes us to a whole new level. These are alloy steels and that’s the family that 4130 falls into. These “alloying” elements do a similar job to the carbon, filling the gaps between crystals of iron with smaller crystals of molybdenum or chromium, still with carbon filling even smaller gaps. The smaller the gaps get the closer the crystals can pack together and the stronger it gets.

But we don’t make alloy steels by carefully placing a crystal of iron next to a crystal of molybdenum and sprinkling on some carbon, instead we melt everything down in a big pot and stir it up. We dig all the ingredients up out of the ground (or recycle them from old cars etc) and they are “dirty”. Back to our tea analogy it’s like someone dunked a biscuit in there. No matter how hard you try some of the biscuit comes off in the tea and ruins it. You can fish the big bits out with a teaspoon maybe, but you can never get it all. Maybe the biscuit was worth the slight damage to the tea, or maybe you can make another cup but this is where the tea-analogy falls down.

The Steel is always going to have a little bit of contamination in there. Stuff like Sulphur and Phosphorus gets in there. In the same way that a tiny percentage of carbon increases the strength of the material a huge amount by gluing the crystals together these contaminants even in tiny amounts can ruin the material. Getting rid of these last few percent of contaminants is difficult and expensive.

So we just mix up the right ingredients in the right proportions and bob’s your uncle 4130? Well actually, no. Once you have all the ingredients together there is a whole range of things you can do with it that will effect the strength a huge amount too. How it is made into a tube is a big factor. Some cheaper tube is rolled up from flat strip and welded all down a seam the whole length of the tube, while the best stuff is “drawn” from a forged blank (seamless). We can also use heat to change the shape and size of the crystals, the permutations of heat and quenching are almost endless. And this is where things get complicated…

When we talk about “strength” we aren’t being very specific. There are different types of strength. A rubber band is pretty strong but it has very little stiffness so it wouldn’t be any use to us. A CD is pretty strong but its easy to bend, it takes a lot to break it but not much to permanently bend it. A stick of chalk is pretty strong (for its weight) but when it breaks it does so suddenly and shatters.

So when choosing a steel for a bike frame we want a mixture of strengths. We want “ultimate tensile strength” (UTS) this is the strength against breaking completely.

We want a high “Yield Strength”, which is the load to permanently deform (or bend) it. We want “fatigue strength” or resistance to repeated loading and unloading. And we want good “elongation” which is how much it can bend before it breaks.

Unfortunately these properties are often linked. Using heat treatments we can fine tune the properties but as the UTS goes up the material gets more brittle, so the elongation goes down and the UTS and Yield strength get closer together and lower fatigue strength. This means that we get less warning about problems. With a super high UTS material the tube might look fine then suddenly break, not good for a bike.

“So that’s great George. I get all that but it doesn’t actually answer the question now does it?”

No. It’s a fair cop. But knowing this will make you a bit more immune to the marketing babble I hope. Now lets look at some specific examples:-

Frame A, is a typical no name Taiwanese clone product from a pub car-park. It may say “tri-moly” or have a sticker on the downtube saying “100% chromoly” but this is pretty meaningless. It may mean that that one tube is 100% chromoly but there are a million materials that would fit that bill and most are rubbish.

Frame B, is an entry level bike from one of the proper BMX companies. The marketing blurb says it is 100% 4130. Now we are talking. It is going to be a reasonable alloy steel tube with the right proportions of Chromium and molybdenum in it. It will be considerably stronger than Frame A but how much of the various impurities are in it is anyone’s guess.

Frame C, is a rider owned company frame. Maybe it is branded 4130 or says ANSI 4130. ANSI means it conforms to the “American National Standards Institute” specifications for 4130. Their equivalent of our “British Standards”, the ANSI have laid down a tight specification for 4130 tube that it will have to have met. The specification will include maximum levels for impurities and probably a minimum set of physical properties. ANSI 4130 will be good stuff. Branded 4130 is also likely to be better than non-ANSI or unbranded tube but it depends on the brand.

Frame D is a top of the line model. The marketing blurb is screaming about the tube, maybe it’s an air-hardening tube maybe it’s not, but the tube is being pushed as something very special.

So which is stronger?

Impossible to say. The strength of a complete frame is down to a lot more than simply what it is made of.

Maybe frame A is made of tube that is half the strength of frame C but if there is twice as much of it then it will probably be just as strong and quite possibly stronger! Though maybe too heavy ever to ride.

Frame D may be made of tube that is 50% stronger than Frame C but if they have used a tube 50% thinner to save weight (remember all these tubes are 95% iron so the weight differences for a given size and thickness of tube are negligible) it wont be any stronger and might well be weaker when you take other factors into account.

So what are some of the other factors? Well the detailed design of the frame will play a big part but that’s getting a bit off topic. In terms of what this article is covering, the big issue is the welds.

Some tube makers marketing will seem to be telling you that their fancy air-hardening tube actually gets stronger with welding! Now that’s an implication that I take with a huge pinch of salt. I mean, what are the chances?

We are talking about a tube that has an ultimate tensile strength close to twice that of generic non-ANSI 4130. It might be sold as a “seamless” tube meaning it started life by being forged into a big blank by having a spike driven through the middle of a huge round slab of material. This forging was then “cold drawn” (“cold” meaning “not as hot as it could be” still pretty hot in my book) through a series of dies over and over again to get it from a short squat donut to a long thin walled tube. This process wasn’t easy and it was expensive. All to avoid the weaknesses introduced by welding up a rolled strip….. But hang-on a second. This stuff supposedly gets stronger with welding!!!???!!!

The drawn tube has also undergone numerous special heat treatment processes; hardening, quenching and tempering to get these amazing properties. But when we weld it we reduce it to a puddle of hot piss, mix it with a puddle of hot piss from the tube it is joining and add in some welding rod. We then just let this cool in the atmosphere with no quenching or tempering… and it’s stronger?!?! I don’t think so.

If we go back to the marketing hype and read a little more carefully we find that “stronger” isn’t really quantified that clearly. This doesn’t mean that the tube is shite. Far from it, but it does mean that you shouldn’t believe everything you read…

Lots of the fancier frames also make a big deal out of the fact that the tube is butted. Butting is where the tube gets thicker in certain parts. A single butted tube is thicker at one end, double butted means it’s thicker at both ends. Beyond that the system breaks down, a triple butted tube could be have a thick bit in the middle for making say a pair of handlebars or it could mean that one end is thicker than the other…

Butted tube means that the tube can be thicker where the welds are and thinner in the middle to save weight, unfortunately it can also mean that the middle part is easier to dent when you drop the bike.

So what does all this mean? What conclusions can we draw?

Well reducing all mankind’s knowledge of materials to one easy to absorb essay with tea-analogy was never going to be a realsitic goal, so now you have to use your common sense. If the maker of the tubing for your frame is prepared to put their name to it, then that’s generally a good thing. Companies like Reynolds have been making excellent tube for a very long time and their reputation depends of keeping the quality up. But equally once that tube leaves their factory they don’t have any control over how it is used. If the frame builder uses tube that is simply too thin and makes an arse of the welds then the best tube in the world is still going to make a crap frame that breaks. The flip-side of this is that some companies can take very basic tube, and by careful design and good quality control, make a brilliant frame that will last a long time.

So in summary good tube is nice but it wont make up for bad design or workmanship. If a company has never made a good frame then just because they are now using “Bobs-Bonza-Butted 97ZZ” wont make it any better. Or if the frame seems too good to be true, for example because it weighs less than a fart, then it probably wont live up to the hype…. But if a company has a reputation for quality and uses some wonder material to make realistic weight savings then it could be a good bet if you can afford it….

Handlebars, Bars, Steering wings. Call them what you like we all need them.

Personally I always find changing bars to be a bit of an ordeal. Not just because I have to wrestle the grips on and not because I have to switch the brake levers, and the cables are inevitably no longer the ideal length. Simply because it changes the feel of the bike so much and I find it hard to adjust. When I finally decided to cut my bars down to a more modern narrow width about 2 years ago it took me the longest time to get fully used to it.

There isn’t much anyone can write to help you acclimatise to the feel of some new bars but hopefully the following blurb will help with everything else.

To minimise the acclimatisation it helps if you can get the new bars on at the same angle as the old ones. To help with this, you can try to measure the old bars before you take them off. Since what really matters is where your hands are, I would suggest measuring from the seat post clamp to the middle of each grip, this will give you an approximate target to aim for with the new set. This is the sensible approach but it never occurs to me until I have already taken the old pair off and am trying to adjust the new ones…

Once you have your new bars in place it is well worth marking a scratch on the stem and the clamp tube so that if they move you can put them back or if you want to adjust them you can tell where you started from. Obviously when adjusting bars do not loosen the stem bolts all the way off, just do it enough that you can tap the bars into the new position without them falling right down…

If your bars are slipping then check the knurling on the bars first. This is the most common cause. Although you might be able to see the knurling clearly enough, a good powdercoat job will follow the troughs and ridges so well that it could still be a very thick layer, and paint is pretty damn slippery. So if your bars wont stay put you need to strip this paint off.

A common mistake with stems is to use the wrong size Allen Key. The Allen Key should fit really well, if it wiggles by a tenth of a turn or so then the chances are you are using the wrong sized Allen Key. Maybe you should be using a ¼” (quarter inch) key (which is 6.35mm) but instead you are trying to use a 6mm metric key, this will inevitably round out the heads of the bolts long before the stem clamps properly.

Width.

The width of your bars will have a big influence on the feel of the bike. Bars can be cut down but they cant be cut “up” (thank fuck I am here to point out the bleeding obvious)… Because of this, bike co’s tend to make bars a bit on the wide side of the average and leave it to you to cut them down. So there is a good chance you will at some point want to cut your bars down.

Ideally you would use a pipe cutter for this. With its big hardened wheels you whizz it round the tube like a pizza cutter tightening the pressure until the end falls off. The problem with this is that most pipe cutters are made for nice soft copper plumbing pipe or mild steel conduit, NOT heat treated 4130. A basic pipe cutter will probably die after one or two cuts, so most of us will instead be looking at the hard-work-end of a Hacksaw.

Now by Hacksaw I mean a full sized hacksaw with a 12 inch blade with nice sharp teeth, NOT a junior hacksaw! Remember GOOD tools are GOOD, and SHITE tools are SHITE.

To stick with the cliché theme this month; measure at least twice and cut once. To that you can add, cut carefully, cut straight and for fuck’s sake don’t cut your fingers off…

Measuring can be tricky too. If you are judging your cut length by measuring the old bars, then remember that the width will measure slightly narrower at the side towards the rider then the leading edge. If you put your old bars on top of the new ones and mark the ends you could well end up cutting too much and leaving them too narrow.

To get a straight line to cut, simply take a piece of paper with a straight edge and wrap it round the tube, if the ends of the straight side meet up then the edge is nice and perpendicular to the axis. Mark it and cut along it. Once you have cut the bars down take the extra 30 seconds to file the burrs off.

Brake levers.

If anyone else out there is still using these quaint old things then you might want to put them on before the grips, particularly if they don’t have a hinged clamp (though thankfully the days of the non-hinged lever seem to be numbered)

Where you run the levers will depend on the width of the bars and how far from the grips you like them. But if your levers are going to be on or close to the bend then you may hit some snags. You might well need to bend the “blades” of the lever out to give you some decent space to pull them. Thankfully this will have very little effect on how they work… Unless you snap them off…

Most people bend their levers out with them still on the bike, and as long as you just need a little tweak this is fine. Just slip a ring spanner over and very slowly and gently bend them out to suit. Keep checking the feel and if in doubt STOP. If you bend them too far then bending them back again is often much riskier and this is when they fail…

If you need to put a really big or complicated bend into the lever then a little bit of heat can be necessary to avoid snapping. But bear in mind that most levers hinge on little plastic bushes that will melt long before the blade is hot enough to help it bend. Brake levers are almost always aluminium and aluminium takes a lot of energy to raise it’s temperature, (high specific heat capacity) so if you are using a blow torch to warm your levers it will take a surprisingly long time to have any effect.

Rather than ruin your plastic pivot bushes and maybe set-fire to your grips, I suggest you take the blades of the levers out and do this in the bench vice. The downside of this is that you cant easily keep checking the shape of the bend without waiting for the levers to cool-down then re-fitting them to the bike. Remember that high specific heat capacity will mean that they take quite a while to cool down and the high conductivity means that they will be hot all along the length and will burn you quite well!

If you do heat your levers to bend them then give the brakes a couple of days to return to full strength. Aluminium “age-hardens” so (depending on the exact alloy) it wont regain all its strength straight away.

There are no guarantees when bending your levers, it’s a risky job whether you do it hot or cold, if you don’t do it very carefully, and even if you do, it might suddenly snap with very little or no warning so don’t come crying to me… You can now buy several levers that are “pre-bent” so one of these might save you a lot of hassle.

Grips.

Grips are also a very personal choice, one mans faithful favourite is another man’s bed of nails. I tried some new grips a while ago and they literally tore my hands apart. Within just a few hours riding I had massive blisters in places I hadn’t got calluses before because I had never really gripped with that part of my hand before.

But whatever grip you choose chances are it will require a good deal of wrestling to get on or off.

Grip wrestling is going to be an Olympic Demonstration Sport in 2008 at Beijing; and by 2012 it is likely to be fully adopted. So there is half a cat’s chance in hell that you could see Russians with huge fore-arms lining up somewhere in dock-lands to put a brand new pair of ODI long-necks onto an Olympic regulation pair of Gay Bars… OK so maybe that’s a bit far fetched… London has no chance of getting the 2012 Olympics…

There are as many opinions on how best to fit and remove grips. Chris Radford (he of the unlimited nose manual circa 1992) used to swear by the “dry” technique. No lube for him, just a good half hour of fighting, which inevitably left the grips not only firmly fitted and ready to ride immediately but perfectly worn in!

Dry is undoubtedly the ideal, but very few people have the shear bloody-minded-ness to pull it off. If you have access to an air-compressor then it becomes an effortless job. Simply work the grip on with a constant flow of high pressure air from a suitable nozzle keeping the grip “inflated” round the bar. Removal is equally simple, with a quick blast of air more than adequate to break it free and float it off.

Surprisingly a lot of people think the purchase of a £100+ compressor a trifle excessive for fitting a new pair of grips maybe twice a year, including me.

Leaving aside the dry or air-lubed options most of us reach for an aerosol. I have heard of people using pretty much anything that comes in a pressurised container with varying degrees of success.

WD-40 is, of course, king of the aerosols. It is the aerosol equivalent of the urban rat, you are never more than 30 feet from a can of WD-40 though you may never know it.

Not surprisingly therefore it is often pressed into service for fitting grips. A job it was never designed for but can sometimes do pretty well. With some grip compounds it slowly attacks the “rubber” and turns them into a slightly gooier stickier compound that sticks pretty well, so it can lubricate the fitting process and eventually “dry” to help hold them on. Unfortunately it is way too easy to use too much and have a bad case of “revver grip”…

Another common choice is spray paint (well it is in a spray can). Allegedly paint will glue the grips to the bars nicely but again you need to wait for it to “set” and if you use too much that could be a long wait, it is also worth remembering that paint overspray can look rather like some idiot has been spraying paint about all over the shop, so probably not best to do it in the living room…

The classic is of course, hairspray. I have a dented can of Harmony “extra hold” that I picked up from those bargain “to clear” shelves of damaged goods in Safeway about 10 years ago which is still half full and has only ever been used on grips. It works great but dries fast so you need to be quick. It also has the undesirable side effect of making your hands smell like a hairdressers in wet weather.

Water also works but takes a very long time to dry.

The common error is washing up liquid… Seriously you do not want to use it. At first it can seem fine, grips go on smooth, but expect permanent revver-grip and if you ever get caught in the rain you will have kids running after the trail of pretty bubbles that are emerging from your bars…

Once you have your bars cut to width, the angle set, your levers bent to perfectly match your grip position, and your grips firmly installed; there is one further job. FIT SOME BLOODY BAR ENDS!!!!

Bar-ends weigh next to nothing, cost very little and could seriously save your life, or someone else’s. As a man who has had a peg punch a chunk out of his hand trust me on this. An unplugged tube is more than capable of causing you serious injury, and a bar-end, even those crappy plastic ones that come free with nearly all grips, could be the difference between getting back up off the floor to try again or rushing to the hospital to have your spleen removed and a lifetime of medication to make up for its absence….

Post Script.

I have had a few e.mails on the subject of grip wrestling since the article came out… This one struck me as being a particulalrly good idea:-

Once again I find myself writing about bottom brackets. Bollocks. I really don’t want to get labelled as some kind of obsessive dude who only thinks about bottom brackets all day long, yet I don’t seem to have much choice in the matter either.

Equally, I imagine that you -the noble reader- is pretty bored reading about them, but you too have little choice but to think about it. If you are in the market for a new frame anytime soon then you will HAVE to choose a bottom bracket. Most frames still come with a USA BB if you just want something you know works (even if it is a bit of a pain to fit sometimes), but most also now come with the option of a euro, some frames only come with a euro and some of the new ones to be launched over the next 12 months will only come with a Spanish or other BB shell.

Once you choose your frame then you are locked in. There is no switching BB size without switching frames or some major re-modelling….

While this is a pain for you it is even more of a headache for frame manufacturers. Imagine you make frames. Maybe you make 3 models in 2 top tube lengths each and 3 colour options for each. That’s 18 different frames to keep in stock (3x2x3) and if you have sold out of blue in one design the chances are you can talk a customer into taking a black one instead.

But now you also have to offer a euro BB shell as well as the USA version, so you have 36 frames to stock (18×2) and if the spanish BB takes off maybe you have to do that too so you end up with 54 different frame designs and you need to predict how many of each the public will want to buy !!! Get it wrong and you could end up with loads of frames that nobody wants and none of the ones they do…

For this reason, there ended up being a meeting of industry types at the subdivision show, with the single aim of thrashing out a new standard. Unfortunately it soon became evident that there is no simple solution in sight.

The main problem boils down to the conflict between metric and imperial crank designs.

A lot of people are running Profile or similar splined cranks. These normally use a ¾” axle which runs in imperial size bearings. To fit these into a USA or Euro BB you have a cup sized to fit and off you go.

BUT we aren’t ALL running these cranks, a similarly large number of people need the greater strength of a bigger axle so there are a lot of Primo cranks out there using a metric 22mm axle and metric bearings, as long as we use a cup of some sort then they can be made to fit in a USA or euro (though there isnt much room left for the actual bearings in the euro).

To add to the confusion we also have some 20mm axled cranks as well as 7/8” and 1” offerings from Profile and Solid respectively.

Fly’s Spanish BB will eliminate the need for a cup by pressing a bearing directly into the frame. But what size bearing should they use? Metric bearings tend to be cheaper than Imperial ones (except in the US) because they are more common, so that is what they have gone with. But for some bizarre reason they haven’t used the existing standard metric size bearing from the USA Primo BB, instead they have adapted a smaller bearing to fit.

The Spanish BB therefore ends up needing custom bearings to run ANY of the popular cranks. They plan on making 2 special size bearings; ¾” and 22mm, which will accommodate Profile race and Primo cranks but if you run 7/8” Profile SS or 1” Solids then you are out in the cold. The only off-the-shelf bearing that will fit is the one to take a 20mm crank axle.

So back to the meeting;

In FBM’s meeting room at Binghampton we all tried and failed to find a simple solution to this problem that anyone could agree on. Fly are a long way down the road of putting their design into full production, so not surprisingly they have no intention of turning back now. Lots of manufacturers are waiting to see how things will pan out; Will the Spanish BB end up needing some sort of reaming after welding to restore the shape? Fly say that the BB shell doesn’t distort at all after welding, if so that makes it a first in the history of engineering and they will have a big queue of motorbike manufacturers asking them how they do it. (Motorbikes use bearings that press directly into the frame, but all these seats are machined AFTER the frame is welded on big fancy machines that cost a lot of money).

We the People are just one example of a major company with doubts over the ability of the frame makers to keep all the production frames as undistorted as Fly claim their prototypes were…

Haro are ploughing on with the Truvative Oversize design mentioned last month. This is like the original photos we saw of the first Spanish BB prototypes when they were using a thread in cup like a giant euro BB. (Ride #72, page 34). By making different cups to fit normal bearings this should be able to cope with most cranks but all the problems that can occur with the euro are still there only your local bike shop wont have the tools to fix them….

FBM were playing it very coy with their own press-fit BB shell. (Theirs simply takes the existing imperial bearings that come with Profiles and if you run any other cranks they wont fit). At the time they insisted it was just an experiment but there was a lot of interest…

S+M seem to be the quietest on this front. As strong proponents of the integrated headset it seems likely that they will try something along the press-fit lines but not surprisingly they are keeping the details to themselves.

So how did the meeting go? Well it was fun and everybody had a laugh but if anything it just highlighted that the “problem” is only going to get much much worse before it gets better….

What is nice to see is that most of these new designs are being offered to the world FREE. There is no exclusive licensing deal (like there is with the “aheadset”), if you want to start making frames with the Spanish BB then you can. You don’t need permission and you don’t have to pay Fly a penny in royalties.

Yorkshire Bottom Bracket

Frame manufacturers HATE bottom brackets. They are an expensive part that needs to be machined accurately to size, they contribute quite a bit to the weight of the frame and in the case of the euro it has to be welded in the right way round and the threads protected during painting and shipping. And they need to do several types to suit all tastes/trends.

This (as much as user dissatisfaction) is why they want a new solution.

Last month I touched on an alternative, using plastic BB cups in a normal American bottom bracket to allow for dodgey fits and distorted shells. Now I have taken the concept a little further and created the Yorkshire bottom bracket.

The Yorkshire bottom bracket needs no precise machining and can be welded into the frame either way round. It is lighter than an American or Euro BB shell and less than 10% heavier than the proposed Spanish BB shell. BUT it is also massively cheaper than any of the others to make, and will accommodate any current crank bearing (with the right cups).

The Yorkshire BB is just a piece of 2” 16gauge tube 66mm long. That’s all.

Because the tube is totally un-modified the tolerance is very accurate without needing any precise machining work. Any welding distortion is taken up by the plastic cups which are themselves ludicrously cheap to make.

Innovative bike companies like Solid, Tree, G-Sport and others who have expressed an interest in bigger lighter hollow crank axles would have plenty of freedom to pick their own bearing size from any catalogue rather than having to fit in round a couple of restrictive custom ones….

Bottom Bracket Key.

Left to Right:-

Euro, Spanish, Yorkshire, USA.

Euro.

Threaded, left and right handed threads in right and left sides respectively. Inside diameter is approx 34mm so the biggest bearing you can get in there is about 32mm.
Outside diameter 40mm.
Typical bearing load capacity 4000Newtons each. Usually fitted with 2 bearings per side. Total theoretical load capacity 16kN.*
Typical weight of shell, cups and bearings:- 280g / 10ounces

Spanish

Internal shoulders. Symetrical side to side.
Inside bearing seat diameter 37mm.
Outside diameter 42mm.
Typical bearing load capacity 6400Newtons each. Total theoretical load capacity 12.8kN.
Typical weight of shell and bearings:- 180g / 6.4ounces

Yorkshire

Just a tube.
Inside diameter 47.6mm.
Outside diameter 50.8mm
Typical bearing load capacity 9400Newtons. Total theoretical load capacity 18.8kN.
Typical weight of shell, cups and bearings:- 300g / 10.6ounces

USA

Usually machined but no shoulders.
Inside diameter 51.2-51.4 ?!?!
Outside diameter 56mm
Typical bearing load capacity 9400Newtons. Total theoretical load capacity 18.8kN.
Typical weight of shell, cups and bearings:- 380g / 13.4ounces

* from this figure you would think that the euro wins hands down on strength to weight, but this figure is for radial (downwards) load. The euro hits problems when you load it from the end (axially) ie. landing a tailwhip or twist or dropping the bike on the pedal…

Since this article appeared in the September issue of Ride UK several new BB sizes have been launched. Most notably the new FBM midsize BB mentioned above HAS been made available and is already selling well. As mentioned it will not accept current bearings to take Primo or other 22mm axled cranks but Haro/Premium are looking closely at it and are making noises about producing custom bearing to do the job….

Nobody really likes public transport. We would all rather drive ourselves to our destination. Door to door with our own timetable and agenda. Unfortunately there is a flip side to this. I am not talking about congested roads or the coming apocalypse of global warming. No. Simply that nobody likes public transport and public transport doesn’t like us…. If you don’t believe me go down to the railway station and ask for a ticket to say London. You may at first think that the guy at the counter is trying to guess your mobile phone number but no, that really is the price he expects you to pay! Now turn to him and tell him you want to take a bicycle with you. He may openly laugh in your face so brace yourself and don’t say I didn’t warn you.

To you this seems illogical. Even if you weren’t an obsessive BMX’er who is probably only travelling to ride your bike, the chances are the place you want to visit isn’t actually Euston station so you need some transport on at the other end anyway. Bikes and trains SHOULD work well together but the train companies don’t want a bar of it…

Before I got my own car I spent many an afternoon arguing with British Rail guards to get my bike on to trains, I also spent a while on platforms waiting for a train that wasn’t too futuristic to let a bike on, or simply giving up and riding instead. Many’s the tale I have heard of half a dozen riders trying to get back from say Nottingham to Barnsley and in the end setting off riding roughly northwards the 40 miles home.

So now I have a nice big car and the railways can go fuck themselves (which is one thing they do seem to be very adept at). But sadly my car can’t cope with large bodies of water like the Atlantic ocean. Trust me, I have checked through the manual and although it does have such essentials as heated wing mirrors and a turbo pressure gauge it doesn’t have a retractable hover skirt or hydroplanes.

So for overseas trips you are pretty much at the mercy of the airlines, and they too have quaint little rules and regulations to follow. The first of these is that if you want to take a bike they are most likely going to want some more money off you. No matter that fat bastards the size of Mongolia can book a single seat at the same price as less cumbersome passengers and that babies under 2 travel free despite making the flight a living hell for everyone within earshot. If you want to stash a little bicycle in the hold they want another random amount of money off you. They will also probably keep this fairly quiet until you come to check-in. So this months technical column is a how-to on getting your bike from A to B without getting stung.

As with any successful military campaign, preparation is everything, though the element of surprise is less important… (Whipping your bike out of your arse at the last minute is more likely to get you shot these days than help dodge an excess baggage fee… so maybe scratch that bit about military tactics…)

Many airlines WILL let you take a bike for free on international flights, but you don’t know which ones until you check, and you probably don’t know which is going to be cheapest until you come to book. So you are left with a dilema. You can either tell the travel agent that you are taking a bike and have her (let’s face it it’s nearly always a girl) check and pre-book for you or you can keep quiet and try to blag it later on.

My recommendation is to play it cool and say something like you MIGHT want to take a bike with you and if so would it be a problem. Being a travel agent they may just make it up on the spot so double check later. Most airlines should say on their websites what the policy is and if it says it’s free then print it out so you can brandish it later on if you have problems.

Having said all this the best bet is for you to pack your bike so well that they will never know it’s there. Specialist bike bags are available with padding in all the right places but they aren’t cheap and they might give the game away by having “Bike Bag” written on the side in big letters. Another alternative that is rumoured to be good is a keyboard case but this and the bike bag can be very unwieldy and if you need to connect by tube or walk far with it then you are in for an epic struggle.

My own bike bag was something I made in advance for a difficult journey I knew was coming. I had to get a bus to the bus depot, then a coach to London Victoria coach station, then walk to the tube and take it to docklands, then another bus to London City airport. The prospect of packing a bike well enough for the coach (let alone the plane) and then manhandling it across London was enough to make me take the problem seriously and make this thing.

In essence it is a plank with skateboard trucks bolted to the bottom, and two blocks of wood to bolt the dropouts to so it stays solid. This plank is stapled into the bottom of a big bag and that’s about it.

You take your wheels off the bike, bolt the dropouts to the wood with some old bolts, zip tie all the bits ,like wheel and bars, to the frame and zip it up.

You may remember that 2 years ago in issue 58 I wrote about the new Euro Bottom brackets that were starting to pop up on some frames. I also predicted that there would be some other new standards to look forward to. Well now they seem to be starting to come through so I thought now would be a good time to try to review the whole lot… Hold on to your hats, it’s going to be dull…

USA Bottom bracket.

The big fucker. These have been with us as long as the sport itself. Originally just a piece of 2,1/8” tube with some spacers turned up to fill the gap between the shell and the bearings. Hammer it together and forget it. Over the years as frames have become more sophisticated the shells have become carefully machined with reinforcing rings and nice parallel faces. But why? Who actually broke a USA bottom bracket shell anyway? Even after years of abuse you could always get the bearings in and out. My current US bottom bracket shell was scrounged of an old Hutch Trick Star and is just 1.6mm thick! It’s a loose-ish fit on most cups and while the rest of the Trick Star was pretty laced, the shell is perfect even after another 4 years in my current frame!

But there is no question that people do struggle with these bottom bracket shells. They inevitably distort as you weld the rest of the frame to them, and with no clear engineering tolerances to make them to, the sizes are all over the shop. My current method for fitting US bottom brackets is to measure the shell then machine the cups back to fit. This gives a perfect fit but not everyone has a lathe apparently?!?

If you just force the cups in then the pressures can be quite incredible. The cartridge bearing can get significantly compressed by these pressures and may not spin as well as it should.

Luckily with such huge bearings this rarely causes them to die and can be an advantage in preventing the cranks spinning while your feet are elsewhere.

Then there is the perception that they are heavy. A big tube with big bearings in is always going to LOOK heavier than a smaller one and in many case it is. With some manufacturers using BB shells that are 3mm thick (twice what mine is) that’s a lot of extra metal to lug around with you. And on a ¾” axled crank like Profiles you have a big gap to fill with cups and bearings so while they are tough the weight can add up a bit. … so what else is there out there?

Euro Bottom Bracket

Despite its relatively recent rise to prominence in BMX the Euro has been around for even longer than the USA bottom bracket. Originally made in French, Italian and English versions with slightly different thread forms and widths there is now pretty much just the one size. Based on a tube about 1.5” in diameter but with a major difference to the US one. It is THREADED.

It was originally made threaded so that the cups could be adjusted. In the days before cartridge bearings when everything used a “cup” and “cone” you could either adjust the cone, as on an unsealed hub or pedal, or adjust the cup.

The first (fixed) cup was screwed into the right hand side of the frame, then the axle fitted, the adjustable left-hand cup set, and locked off with the locking ring.

Over the years for some bizarre reason this is the size that most normal bikes have gone with. It has caused plenty of problems in its time, but being a fairly standardised thread there is a size to work to so the sizes haven’t drifted around like they have with the USA BB. As a result there is rarely a huge problem putting a good new one into a good new frame, and if there is there are taps to chase the threads out of the frame and ensure a smooth assembly.

Mountain-bikes and road-bikes have long since moved on to sealed for life units, with axle and bearings all tied up in a single package. You screw it into the frame and when something goes wrong you replace the whole damn thing. Shimano have made a fortune. But in BMX things are a little different. We want to squeeze our big strong cranks in there and then treat it like shit. We want to do big jumps and land hard and there is no suspension to cushion the blow.

So we still have two separate cups but now holding cartridge bearings. We screw in the fixed cup the same as it ever was and then we screw in the adjustable cup and lock it off with the lock-ring. But this is where a lot of the problems start.

The cartridge bearings will spin smoothly over a large range of adjustments of that cup. But if you screw it in too tight you will be pre-loading the bearings something rotten (see issue 75 for stuff about spacer tubes). Add after a few side-load-impacts, from 360s and tailwhips, the small bearings can soon blow-up.

There is a simple and elegant solution to this particular problem. The Gusset cranks that come with a euro BB also come with an extra set of spacer tubes to space both the inner and outer bearing races. As long as both inner and outer spacers are the same overall length you should be able to crank the adjustable cup up as tight as you like without ever pre-loading the bearing.

The remaining problems with euro BBs are mainly to do with neglect and abuse. If you always use the right tools and do everything by the book they should be fine. But let the cups corrode into the frame, or put the wrong side cup in the wrong side of the frame and you are in for some major headaches.

Put a big dent in the bottom bracket shell and unscrewing the cup may become close to impossible. With smaller bearings that do break much more frequently than their USA alternatives this is likely to be a more common occurrence too, so there are more opportunities to get it wrong.

There is a small but significant weight saving to be made but we close the door on many future weight saving possibilities. Even a 22mm spindle struggles a lot to fit in there, and the bearings become ludicrously small, there would be literally no chance of moving up to a bigger, hollow-er, lighter crank axle.

Spanish Bottom Bracket

A lot of thought has gone into the new Spanish bottom bracket and still it isn’t ready for release but we are told it has settled on its final size. Originally shown as an oversized euro with threads and cups it has now evolved to a cup-less design with a cartridge bearing pressing straight into the frame.

The loss of the threads can only be seen as a good thing. The problems of pre-loading and thread damage are immediately gone and it is likely to be cheaper to produce and saves shops having to buy expensive taps for cleaning a new size of thread.

The logic of putting a bare bearing straight into the frame is simple. Bearing units are already made to astonishingly tight tolerances so there is no issue over size. The 37mm bearing will be so close to exactly 37mm that it would require some fancy measuring equipment to determine just how far off it is.

With the size issue settled, they only need to make the seat in the bottom bracket shell to a hair under 37mm (say 36.95mm) and the bearing will tap in with just a gentle resistance.

Perfect…? Well maybe not. As with any other bottom bracket shell the Spanish version will be welded into the frame, there is therefore inevitably the possibility of the shell distorting under welding. A shell machined to 36.95mm might move slightly out of round as the down-tube, seat-tube and stays are welded on and the rest of the frame tries to pull it in different directions. So they will probably need to be welded on then reamed and faced back to size. This is no big deal as long as it is done, but may add some cost.

The other issue is the size itself. 37mm is a little smaller than I would have liked to see them use. You wont find bearings to suit ¾” or 7/8”cranks like Profiles on any bearing stockists shelf. Nor ones to fit 22mm Primo cranks.

Fly are confident that the bearings will become common place and fairly cheap with time but they are unlikely ever to be made in the kind of numbers bearing manufacturers consider good so there will always be a slight premium to pay. There is again little scope for crank innovation. You can get a 37mm bearing to take up to a 25mm axle but the bearings are getting close to their limit and the strength wont be fantastic. My other worry is that bearing modified to fit will be a little thin in places and may shatter unexpectedly.

I would have much preferred to see them go with a slightly larger 42 or 47mm bearing, so that stock bearings in a lot of axle sizes could be slid straight in there and others accommodated with a small cup… But I guess that puts us almost back to the US bottom bracket and leaves the door open for the same old problems of fit.

Megatech Bottom Bracket

You may not have heard of this one. Similar to the Spanish bottom bracket, it has been around a long time but hasn’t really caught on yet. Using a 47mm bearing with a 27mm crank axle it ties the frame to a limited range of cranks. Not seen any sign of it on BMX yet but if you do, now you know what it is.

Truvativ Bottom Bracket

Truvativ make a thing called an ISIS overdrive bottom bracket. Using the ISIS standard which has become fairly popular with mountainbikers and some flatlanders and can also be used with a euro bottom bracket system.

The overdrive is threaded like a euro but at around 48mm compared to the euro’s 35mm they can fit some bigger bearings in there. The problems of thread damage are still there but because this is a sealed unit there are no problems with bearing pre-load. The ISIS system means you aren’t going to be fitting your existing Profile and Primo cranks straight in there unless they bring out some other versions of the bottom bracket. Haro seem to be heading in this direction but I don’t have any details yet.

George’s Bottom Bracket

Finally. Its all very well for me to sit here picking holes in all these systems but can I do any better? Maybe I should shut the fuck up until I have an alternative to offer? Well as it happens I do. How about we all stick with the USA bottom bracket, make the shell thinner to save weight and agree on some tolerances for the bearing cups and shell!?!

In the absence of this common sense approach there is a simple cheap alternative, which I have done in the past and works really well. Just make the cups out of plastic. Being significantly softer than the aluminium we have now it can accommodate a much larger range of sizes. The steel bearing and shell can squeeze the cup to relieve some of the pressure on the bearing and they slide in and out very easily. Distorted bottom bracket shells make no difference, plus they are less than half the weight. I first made a set of these for Ben White about 4 years ago and they worked a treat….

If you have waded through all this twaddle then well done and I hope you get over your insomnia soon…

Suggestions and requests for future tech columns gratefully received…

Someone requested that I do a tech column on head angles and steering geometry. I wasn’t sure at first if this was a worthwhile subject, after all, there isn’t that much variation available is there? Most frames have a head angle of 74 and a half! Degrees and most forks have one and a quarter inch legs with dropouts that stick out just enough to get a peg on.

Granted the odd frame has a 74 or 75 degree head angle and there are so called “flatland” forks that have less rake but by and large they are all the same… or are they?!? Dun-dun-durrr (dramatic/sinister drum roll).

To understand what is going on with steering geometry we are going to need a picture or two. There are two main controls over steering feel. The one we are all familiar with is head angle and the other is fork “rake” or off-set.

The key thing to look at it is the red line. This is the “steering axis” it runs through the centre of the headset bearings and is the imaginary line round which all the steering components turn. OK maybe I am dumbing this bit down a bit too much, but it is crucial that we get this part clear. The head angle is the angle this line makes with the ground.

Notice how the “head-angle” is measured relative to the ground; not relative to the top or down tube or any other part of the frame at all, only relative to the ground. This is fairly obvious, but when you take the time to think about it you realise that this means that all sorts of parts that are nothing to do with the frame CAN and WILL influence the head angle.

Stick an old school 1.75” freestyle tyre on the back, and compared to a 2.2” knobbly up front, you might lower the back end by over half an inch. On a typical bike that half inch will translate into a change in the head angle of 0.8 degrees, so your quoted 74.5 head angle becomes 73.7 !!!! Tyre size isn’t the only factor that will alter the head-angle; different forks have different specifications for the distance from axle to headset, and some headsets are thicker than others.

Add together the effects of tyres, forks and headsets and your head-angle could be over a degree off the maker’s original intention! Yet another factor to consider is whether your frame even has a 74.5 degree head angle to start with!

Everything that is ever made is subject to variation, even the most precisely made components are given a tolerance within which they can vary; a 20mm bearing is very precisely made but it is still allowed some leeway, so it might be as big as 20.01mm. Bearings are precision ground to size; bike frames are (relatively) roughly machined tubes welded together. Welding always produces some level of distortion so you can bet that no two frames have precisely identical head-angles.

74 and a half degree is a pretty specific size; over a 4 inch long head tube the end of the tube only has to wonder off by under half a millimeter to change the head angle by quarter of a degree. It is therefore pretty likely that most mass produced frames aiming for a 74.5 degree head angle will actually be anywhere from 74.25 to 74.75 and perhaps even further afield…

Bollocks, burnt my pizza… anyway, where was I?

Oh yes. So petty as it may seem, these variables mean that a new fork or tyre or headset can feel more different than you might have expected. Treat yourself to a new frame and parts that should have the same head-angle and it may surprise you how different it can feel.

So now I have convinced you it is worth thinking about, lets get back to it.

Now imagine we have a weird frame with a 90 degree head angle and “zero rake” forks. That would look like this (fig.1.).

On our example vertical head-tube frame with no rake you can imagine that as you turn the bars everything rotates around that red line, and since that red line also passes through the point where the tyre meets the ground (marked with the red cross), we would have what is called neutral steering with no trail.

Now lets imagine a normal frame with say a 74 degree head angle, but still with “zero rake” forks (fig.2.).

As before all the steering parts “orbit” around the red line, but now you can see that the effect of leaning the head-tube back has been to move the point where the red line meets the ground so it is ahead of the tyre’s “contact patch” (blue cross). This creates what is called “trail”. The tyre “trails” behind the steering axis so creating some stability. This is kind of like the rudder on a boat trailing behind and kept central by the drag of the water. In the same way; as we ride along, the drag on the tyre tries to keep it as far behind the steering axis as it can, this makes the steering tend to self straighten.

But, we could get this same effect with the vertical head angle just by having the wheel off-set backwards a bit (fig.3.).

So why don’t we?

Well there is another factor to think about… By leaning the head angle back we create stability not just through “trail” but also through the effect of gravity. With a reclined head angle and forward offset dropouts (fig.4.) we can create a situation where the rake on the forks causes the front end of the bike to lift slightly as you steer.

In much the same way that water flows to the lowest available level so too your weight on the bike tries to settle down. With the forks turned, the bike isn’t as low as it could be so the effect of your weight is to straighten the steering. This can be pretty hard to see so let me put it another way.

If you turn the bars through 360 degrees the bottom of the tyre would sweep a circle, but this circle would be perpendicular to the head-angle not flat to the ground. The back of this circle would be below ground level by a fair bit. Obviously we cant have that so the front of the bike has to rise up to allow it. If the bike lifts then you lift, so to turn the bars 180 degrees you might have to lift the front end of the bike by an inch or so. Equally if you let the bars return to straight forward the bike drops… just like water flowing down hill this is a more stable situation so it will tend to this position.

These two effects work together to create steering stability, but while the trail only works when you are in forward motion, the laid-back head-angle-effect is independent of speed or direction.

This summarises how the steering works but we also need to bear in mind that leaning the head angle back and adding rake both work to increase the overall length of the bike too. This will obviously make the balance point for front wheel tricks different but there is also the effect this has on the bikes rotational inertia (how hard it is to do a 360 say) and the much more confusing gyroscopic effects.

Over the years we have settled to the small range that our bikes currently make use of. We like a small amount of trail and so reasonably quick and responsive steering and we like how the other factors work out at this position.

Some flatlanders like a fork with less rake, by looking at these diagrams you can see that this results in more trail and so more speed stability, but less gravity based stability, so at low speed this can seem “twitchier”.

So what earthly use is all this to you? Probably none, but although it is easy to think that these small adjustments make very little difference the truth is that any slight change is very noticable.

While in some ways it is ridiculous to specify a head angle accurate to half a degree when it probably isn’t made within much less than a quarter degree of target we might as well aim for the ideal. At the end of the day steering feel is always going to be a very personal choice. Hopefully the above twaddle will help you choose your next frame or fork with a bit more certainty about how it will ride, and even cross your mind when buying a headset or a pair of forks or even just a tyre.

As we the riders take control of our sport these are the things we may want to know, maybe in the future fork manufacturers will declare the fork leg length (centre of dropout to bottom of headset) so that we can know how it will effect the steering feel…. Then again maybe we wont be that arsed…

Once again I find myself sitting in front of the computer wondering how to start my tech column. Every few seconds I turn my head to look out the window for inspiration… or is it distraction.

How the hell do you write a thousand words in such a way that people want to read them? How do you compete with the other hundred odd pages of pure quality journalism in this magazine? How do you write on the subject of a small thin tube and not loose the readers interest after just one paragraph?

Well this month’s literary gambit will be much like previous months, I will swear and rant and hope you see the truth behind my rambling bollocks. Chances are you wont, and you will carry on in the same old way, but eventually things will catch up with you and when it next breaks you will remember my words and do it right next time.

So once again I return to the heart of any bike; the cranks. Specifically three-piece cranks with sealed bearings. There are several problems people have when working on their cranks and most stem from the same thing.

The bastard manufacturers don’t give you any shagging instructions with the fuckers! A hundred plus quid on some twating cranks and the cunts are too damn cheap or lazy to put a black and white A4 sheet of instructions in with them! Or, if they do then they don’t actually help. How hard would it be for them to put a detailed photographic guide on their website?!? Maybe they could actually use flash for something useful for once… Deep breath.

So to make up for this shortfall, this month I will try to cover some basic concepts.

First off, the dreaded “spacer-tube”. The questions on everybody’s lips seem to be; “Do you need to use the spacer tube?”,” Will it work without it?” and “which tube do I use?”

The short answers are “YES, for sphincter’s-sake use the bloody spacer tube.”, “Probably not for long” and “The right one.” To understand how, why, what and which, let’s review how it all goes together.

Whether you run a USA or euro or some other new and wacky bottom-bracket they all work pretty much the same way. Determining how it all works is the width of the bottom bracket shell.

In the first cut away view you can see that everything on the axle should butt up to everything else with no gaps. Let me emphasise that; NO GAPS.

This is so that when you tighten, for example, the right-crank-axle-bolt; it pushes the crank arm against the sprocket, and the sprocket (with top-hat spacer) against any extra spacers on that side. These spacers in turn press against the inner race of the bearing, which presses on the infamous spacer-tube, which presses against the far bearing’s inner race. The inner race then presses on the other side spacers which press on the left crank arm which is held in place by its own end bolt.

The force in the bolt can therefore be transmitted through all the parts on the axle to the far bolt which is screwed into the axle too and the “circuit” is completed.

IF however the spacer tube was removed the force from the axle bolts has only one way to get from one side of the bottom bracket to the other. Through the bearings! Without the spacer tube the force has to press the inner race against the balls, then the balls have to press against the outer race, then the force can work its way through the BB shell and back through the other side bearings.

As discussed in the hidden-headset article two issues back, this “axial” load is not something a normal bearing can cope with very well. With the bolts done up tight this force could be well over a ton; add to that the impact forces from tailwhips and 360s or even just dropping your bike and it’s no surprise that the bearings can die very fast, especially on the tiny bearings in a euro bottom bracket.

So how do you pick the right spacer tube? Well the easiest way is to put the likely candidate on the crank axle and put the bearings on each end. You can then put this assembly up against the BB shell itself and have a look if it seems right.

The lips of the two bearing cups must be WIDER apart than the BB shell. Ideally this should be just half a millimetre or so but 2 or 3 millimetres is fine. DO NOT be tempted to go with a width that is just under the width of the shell. If the spacer tube is not compressed then it is doing nothing and the bearings will suffer. On a USA BB it is fine to run with one cup sticking out slightly, although it looks dodgy this is absolutely correct.

With a euro BB you will need to adjust the “lock ring” to fit and hopefully “lock” everything in place, if this lock-ring slips later on then the loads can build up on the bearings and kill them, so keep an eye on it.

If you don’t seem to have a suitable length spacer-tube in your set, then you can use the shorter one and one or more of the smaller external spacer washers to make up a custom length.

For cranks that don’t have pinch-bolts this set-up is essential and the only way that will give decent bearing life.

But some people want a little stiffness in their crank bearings, they want the crank arms to stay still in the air, and taking the spacer tube out will give this. Although it isn’t recommended you can get away with this on cranks that use pinch bolts (like Primos). Because the end bolts aren’t needed to keep the crank arms on, you CAN run these cranks without the spacer-tube. In this situation you only want to tighten the end bolts enough to install the cranks and set the “resistance” in the bearings; then lock the arms in place with the pinch bolts. On a USA bottom bracket this should work fine and let you keep a little stiffness in the bearings without risking killing the bearings too fast. On a euro BB you will have to be a lot more careful, the bearings (especially the smaller ones needed for cranks like Primos which have pinch bolts) will still be at risk of axial overload. Any impact on the end of the cranks will now only be transmitted through one bearing (since the other is free to slide on the axle).

While we are on the subject let me emphasise a few other points.

With splined non-pinch-bolt cranks (like Profiles) use as few spacers as possible so that there is as much axle inserted into the arm as possible. The less arm you have inserted the more chance there is that the cranks will wear the spline and become loose. Also over time it is easy to only ever tighten one side of the axle. Without knowing it, you can be pulling the axle over to one side leaving the other arm with very little axle inserted.

Most cranks are designed with the intention that NOTHING goes between the sprocket and the crank arm, this includes the “top-hat” spacer. If you put a spacer in this gap then you must put one of the same thickness on the sprocket bolt. This is the most common cause of this bolt always coming loose.

Remember that left pedals and right-hand euro BB cups have a reverse thread.

Well that about wraps it up for this month, I hope this twaddle was of some use to someone, and if not… well at least you had something to read during that long session on the shitter after a questionable curry… (difficult with the internet version though I admit…)

The progress of civilisation is based upon one thing above all others, Albert Einstein put it very well when he said that “If I have seen farther than others, it is because I was standing on the shoulders of giants.”

In other words one persons progression is based upon the work done by the people who went before, and many of today’s pros can thank the old school-ers for paving the way. I remember watching my first BMX video, it was Agroman and just by watching it we improved. I can remember watching Matt Hoffman double pegging one of his first rails then re-winding it and watching it again and again in slow-motion to help me do my first rail. Cutting out the bullshit, we all know that you can learn from other people’s riding in videos, photos and magazines. And what’s more you can learn from watching your own riding back to see where you went wrong. In short we all like to take pictures and video for a whole range of very good reasons as well as just pure vanity.

With the coming of digital cameras we are now freed from the hassles of taking the film in to be processed only for them to not develop the last shot on the film; put stickers all over them explaining how YOU messed up the photo when the truth is they cant develop a picture; AND charge you a fiver for the privelege.

Now serious photographers will generally tell you that film is the way to go. They used to tell you that digital was worthless, but as the technology improves most are compromising at least a little bit in their critisism. This alone tells you how good they are getting.

So like many other riders I embraced the digital camera some time ago, I fancied the immediacy of seeing my picture straight after I take it and I fancied being able to take short video clips, but digital cameras have one MAJOR problem from a riders point of view. SPEED.

Take a picture with a normal film camera and the shutter opens to let light onto the film straight away. The moment that you pressed the button is the moment that gets photographed.

With a digital camera this is NOT what happens. Now I am not going to try to explain what does happen because frankly I don’t have much idea about it, but suffice to say that you press the button and get a picture of the riders arse from a half second later as they leave the frame. This can be absolutely infuriating, you end up having to press the shutter release as the rider leaves the lip to get a shot of the actual jump or whatever. A lot of this “shutter lag” can be avoided by getting the camera to do some of the work before hand. You can pre-focus and set the exposure etc. by half pressing the shutter button, but still you end up with a significant delay which can still screw up your photo.

If you are in the market for a digital camera then obviously there is a shit load of information on the web, sadly most of it is about taking pictures of bowls of fruit and test-cards. Want to know how distorted a picture of a sheet of paper will look like from 2 feet away? Well it’s your lucky day. Want to know how long after you press the button it will take a picture? You will have to look a lot harder to find out and often you wont find an answer at all..

So seeing as I was in the market for a new digital camera, and seeing as I was going to be doing all the donkey work to find one suitable for taking action shots of BMX, which I guess is what you might well want one for two, I thought I would share the experience in a mini review.

My wish list was for a camera the size of a match-box, that would take absolutely perfect photos, in any conditions, high speed sequences and broadcast quality video with dolby surround sound and cost 20 pence. Obviously I was shit out of luck so I had to look for the closest match that actually existed.

My researches on the web showed that the best I could hope for was a short shutter lag and a sequence mode of 5 frames per second, which is excellent, coupled with 30 frames per second 640 x 480 video clips with sound, Fuji seemed to have the lead. But when I got my hands on the camera I was a little disappointed. It delivered the promised 5 frames per second at full resolution but could only manage it for 5 frames. This is great for shots of jumps and airs to pick the most tweaked but most tricks last more than a single second so you can never capture the whole thing from start to end as a sequence.

The video mode was also very good, but pan quickly and the camera has trouble keeping up with the action without blurring the edges. The ordinary pictures themselves were great but I was still having to make quite an allowance for the ever present shutter lag. My search continued. Recently my attention was drawn to a new range of cameras from Kyocera. Kyocera claim to have cracked the shutter-lag problem with some new technology that they call R-tune. Fuck knows what this is supposed to stand for but frankly who cares, but they claim it will reduce shutter-lag to much the same level as a mechanical film shutter which is about all you could ever hope for.

But that wasn’t all they were claiming, this same R-tune technology allows the camera to take sequences at three and a half frames per second for as long as you like! Let me emphasise that; “FOR AS LONG AS YOU LIKE”!

Or at least as long as you have space on the card. This was what really caught my attention. So I decided to check it out.

There are 3 cameras in the new range from 3 to 5 megapixels, but the dinky little 3 megapixel sl300r is slightly faster at 3.5 frames per second than the bigger 5 megapixel s5r which only does 3 frames per second in it’s sequence mode. Now half a frame per second may not sound like a lot but for most tricks it will make a huge difference. For example a 3 frames per second motor drive on a conventional camera only caught 3 frames for a 22 step rail on a conventional film camera. So that extra little bit of speed is much appreciated, and that’s the one I decided to test.

Not being restricted by the layout of a film cassette digital cameras can be all sorts of weird shapes and lay-outs. With the sl300r, Kyocera have made use of this by hiding all the zoom lens and focusing mechanism inside a weird swiveling body the size of a pack of playing cards. Although this looks like a gimmick it actually works really well and means that there are no exposed moving parts.

So the big question is how well does it work?

Well, over the 4 weeks I had it to test we had mainly rubbish weather and overcast days, so half the pictures were taken indoors and the few outdoor ones at the new Warrington park in very dark overcast conditions.

Unusually for a small digital camera you can adjust nearly everything manually, the iso can be adjusted from 100 up as high as 800 to help in these dark conditions but at the expense of increased grainyness. Aperture can be set manually but only to 2.8 or 7.5. With my previous digital camera, taking a shot of a jump required me to “pre-focus” and set exposure and shutter speed by half pressing the shutter release button while looking at something the right distance away. This often isnt easy and if you don’t like the settings it chooses it’s tough luck. I would have to turn, half press the button then hold it there, wait for the rider then press the button the rest of the way a fraction of a second before the peak of the jump. Then I would have to repeat the same proceedure for the next jump since the setting would be lost.

With the sl300r the manual settings let me sort out the focus and aperture and leave them set, then I just have to halfpress to get the shutterspeed set. With this done the picture really did take the instant I pressed the release. Capturing the peak of an air or the point of maximum extension of a variation is suddenly easy. On this count the R-tune thing definitely seemed to deliver.

In the sequence mode you have all the same adjustments but flash is obviously out of the question because there is no way it could re-charge in time, so the camera automatically disables it. To be honest this is no hardship, the built in flash is pretty weedy anyway.

To test the sequence mode I went to the new Warrington park (which is good but has some problems) and persuaded Mike Taylor to do a few sequence worthy tricks despite the wet weather. Unfortunately the dark overcast day wasn’t ideal but the camera coped very well capturing some excellent sequences at the claimed 3.5 frames per second for a good 5 frames, the limitation after that is how fast the camera can write to its SD memory card, with a fast enough card it should be able to keep this up until the card is full but you need a super fast card which I didn’t have. By the time the camera is actually launched these cards will be available but you will have to be sure to get the right sort.

Video Mode suffered from similar problems, at the higher resolution and 30 frames per second the slow cards couldn’t keep up, but knocking back to 15 frames per second there was no problem. Image quality wasn’t all I could hope for in the video mode but it didn’t seem to suffer as much blurring of fast motion as some others.

Overall I was very impressed, the camera did everything it claimed and took some good photos. With new models coming out seemingly by the week this is the first I have come across that really addresses the needs of BMXers (hence the review). So if you are looking for a small digital still camera to document your exploits I would keep an eye out for the R-Tune cameras….

Follow-up…

Since the test I decided to buy the slightly fancier “Contax” version of the camera, a fast card and a wide angle adaptor lens. The Contax version, the SL300R T* has a specially coated lens that seems to improve image quality quite a lot. The sequence mode has really impressed me, averaging 3.75 frames per second at full resolution in my test it really lets you capture some great sequences that no other compact, cheap(ish), camera could…

What the hell is a Hidden Headset?
Good question. And surprisingly hard to answer.

Fifteen years go when I became a born-again BMXer, headsets were utter utter shite. You had two choices, a Tioga Beartrap in a size that fitted, or a Tioga beartrap in a size that didn’t fit. These were all one inch threaded headsets but for some reason there were several sizes to choose from, getting the right one was always a pain. Once you had your headset fitted you then spent most of your time tightening it. After every ride it was loose, shit, it was probably loose five minutes after you started riding. This was only 1988 but headsets were working on technology from 1888, or rather NOT working on technology from 1888.

Then came the Aheadset, no threads, YAY! One size, YAY! Stronger forks, YAY! Stems that didn’t slip all the time, YAY! At last we had a standard to embrace, OK so it still used a rough-arse unsealed bearing and it was still a bit weak and flimsy, but it was undoubtedly forward progression. Over the last ten years we have grown complacent and forgotten all about the nightmare that was small threaded headsets; cups have got stronger and most people can go months without touching their headset.

But now things are changing again, lots of frames are boasting a HIDDEN headset and loudly proclaiming it to be a huge leap forward. Hooray! But hang on a minute… What is so aesthetically displeasing about the aheadset that we now need to “hide” it? Is this a real step forward or change for change’s sake?

Balls

We are all familiar with the terms “ball bearing”; “sealed bearing”; “un-sealed bearing” etc but they are often misused so lets clear up the definition first.

Sealed bearing; This is what most of us think of when we hear the words “sealed bearing.”

A fantastically well made rolling element cartridge bearing, precision ground to a very high tolerance so that it needs no adjustment and just spins beautifully. Two little rubber shields keep some of the crap out and they fit into a housing that is usually a slightly tight fit. They aren’t actually “sealed” but they are at least bearings.

Sadly most headsets don’t use these. Instead we have an array of balls loosely tied together by a soft metal “cage” to make a ball necklace that we drop into a cheap steel cup. A “cone” then sits on top and we adjust the assembly to take the slack out.

So why don’t we use “sealed bearings” in headsets? Well the type shown above just wouldn’t be up to it, although they are big and beefy they are designed to take mainly “radial loads”, ie. loads at right angles to the axis of rotation. Like wheel or pedal bearings. They can take some small axial loads more than enough for a wheel say which only gets an axial load when you bang the wheel sideways into the ground, for example fluffing a tailwhip. If you cut one in half it would look like this:

As you can see the contact points are at the inside and outside of each ball so this is the direction it can best carry loads.

But there are other cartridge bearings which ARE designed to take big axial loads. These are called “Thrust” bearings. A pure thrust bearing can take huge axial loads so it’s the sort of bearing you put at the end of a ships propeller shaft to take the thrust from the propeller and use it to push the ship forwards.

BUT a pure thrust bearing can take almost NO radial load. Cut in half one would look like this:

As you can see this sort of bearing can just fall to bits and needs to be loaded to hold it together, and the contact points are top and bottom.

So for a headset what can we use? Forks take a lot of force straight along their length but they also take sideways and head on impacts that cause big radial forces too…

Well there is another type of cartridge bearing called an “Angular contact bearing”, these look more like this:

With angled contact surfaces they cant take radial loads as big as a pure radial bearing or thrusts as big as a dedicated thrust bearing BUT they can take pretty big loads in BOTH directions unlike either of the others.

This is the basic bearing arrangement used in nearly ALL headsets. In our current cheap Aheadsets the outer race is built into the cup and the inner is the cone. But you can also buy fancy ones where a cartridge unit, that looks a lot like the one above, is employed and sits inside a separate cup and cone which act simply as seats.

So since these newer headsets have a separate bearing-race and cup, somebody realised that the cup was now only acting as an adapter to let the headtube hold the bearing unit. And that if the headtube was made bigger and had the precise bearing seat built in the cup would no longer be necessary.

This would result in two less components which is obviously simpler and lighter, it also means that the headtube can be a little longer to reach the normal position where the bearing would sit in its cup. This means that the toptube and down tube are welded a little further from the end which can help reduce distortion.

If this was the whole story then there wouldn’t be anything to worry about, but there is more. It is an unfortunate fact that when you weld things they tend to distort. SO when a headtube is welded on it tends to become slightly oval. The traditional solutions to this are either doing nothing and hoping the tight fit of the cup sorts it out; OR to ream and face the headtube. Reaming and facing is fine for high end frames but it needs to be carefully allowed for, plus it adds cost. Reaming and facing an actual bearing seat is much more difficult so the manufacturers of Hidden headsets have tried to design the problem out.

This is a representation of what a hidden headset would look like sawn in half.

As you can see there is a very slight gap between the bearing unit and the headtube sides. This means that you will never have to hammer your bearings in or out; Woo-Hoo!

Instead the bearing unit sits on a forty five degree chamfer. As the top bolt is tightened the bearing unit settles down into this conical seat which matches a conical chamfer on the outside of the bearing.

This ridge on the inside of the headtube isn’t the easiest thing to make, hence the increased cost of a frame with a Hiddenset BUT it does add considerably to the rigidity of the headtube, Flareing resistance is increased and the headtube is less likely to deform during welding.

The downside is hard to explain but I will give it a go.

The first biggie is that the frame needs to be well made. As long as the hiddenset is mainly on the top end bikes it will probably work very well, but on cheaper bikes with a higher tendancy to distort under welding, things could start going wrong. IF the headtube does distort from round to a slight oval then the bearing will not sit on its forty five degree ledge properly. It may touch only at the sides while the front and back sit a little away from the seat. This would manifest itself as a very slight wobble under big loads. Every time you hit a ramp it might click or groan. As time went by this movement would reduce the bearing unit life drastically. And if it was run with broken bearings all the usual problems of flared headtubes would be likely, only mending a hiddenset headtube is likely to be even harder then an ordinary frame.

Another consideration is also related to wobble. If the headset is even slightly loose then the bearings can wobble around in their seats; in the same way a funnel can rattle about in the neck of a bottle. If this isnt corrected then it can wear the seats or even flare the headtube. Lastly we should consider that the Hiddenset wasn’t developed for BMX, it wasn’t even designed for mountainbikers. This is road-bike technology! Those skinny but fit guys who hammer round the Tour de France are undoubtedly hard on bikes in their own way but it is very different to us scum-bags launching off ramps, steps and dirt jumps into oblivion.

Campagnolo who make the Hiddenset used to make BMX racing parts many many years ago but they dumped us when things got tough in the Eighties. If the hiddenset isn’t a success with road racers they wont keep it alive for us BMX peasants…. So, if you are thinking of going for a frame with a hiddenset bear this in mind, if it doesn’t work out there is no way to go back to a normal headset.

A few months ago I did a tech column moaning about how the parts for your bike often don’t fit together very well, hopefully some people found it interesting but I later realised that it wasn’t a fat lot of use to most riders. So this month, rather than rattle on about some deep technical issue, I thought it would be more helpful to describe some of the less well known “tricks” that can make your life a hell of a lot easier when it comes to mending your bike.

Now I could write an illustrated guide about how to change one particular aspect of your bike but there are so many variables that it just wouldn’t be that useful. So instead I am going to talk in depth about some general techniques that will work in a lot of situations, so hopefully next time you hit a snag you can “think” your way round the problem before resorting to brute force.

But first a friendly disclaimer. Existing is dangerous. Leaving the house is practically an invitation to disaster. Working on your own bike is the virtually suicidal. You might as well go and drop your scrotum into a blender as even consider picking up a spanner. Tools and bike parts can break and fly up to maim or kill you. It’s your bike, you are in control of your own actions, if you choose to work on it yourself then you take any and all risks for yourself. Wear protective eyewear at ALL times, even in the bath, removing your full face helmet at anytime is entirely at your own risk. You should always have a fire extinguisher at hand and the assistance of a trained paramedic available. I and Ride BMX magazine couldn’t give two shits if your bike works or not, so if you manage to cock something up and mangle yourself into a paste please do not go crying to a lawyer, it’s your own damn fault…..

Number 1. The Spreader Trick.

Pinch-bolts are a common feature of many bike parts. The backs of stems are the obvious example but you also find them on cranks, seat-clamps and some brake levers. One side is threaded while the other has a recess for the head of the Allen bolt. When you tighten the bolt the two halves are drawn together and shit gets clamped. But, when you come to undo them the part does not always spring apart again, so the stem or crank arm can be a bitch to remove. In this situation many people will reach for a screwdriver and jam it in the slot to lever the two sides apart. This often works but is awkward and makes a mess of the part. As long as the hole is threaded right the way through this is the time to use “the spreader trick”.

Loosen off all the bolts then remove them all the way from the part. Then take them round to their opposite side of the part and start screwing them directly into the tapped side. Now you just need to insert a suitable bit of “stuff” into the slot for them to push against, you can use a flat spanner or a coin or any old piece of scrap, but whatever you use is likely to get marked and damaged so don’t use your best cone spanner or anything!

As you turn the bolt the two sides get forced gently apart and the part should loosen off perfectly.

This trick is particularly useful if you have a “pinched” stem and need to insert a shim. When a stem has pinched at the back it looses nearly all its clamping power. The face that the head of the bolt sits on is no longer perpendicular to the thread of the bolt so lots of power is wasted. If you just try to add a shim without spreading the stem then it can be a nightmare to get together, but using the spreading trick you can open the slot slightly past its “correct” parrallel sided position and get a nice few layers of shim (cut from a pop can) in there.

The Spreader Trick is a good one but you can overdo it. On cranks that use a big fat spline it can help with removal, but if you do it too much you can actually make it HARDER to remove the arm as the splines nearer the pinch bolt “twist” in their grooves and jam like a wedge. It is very tempting when this happens to spread the slot even more but you will only make things worse, so back off and if things don’t improve, even try putting the bolts back the ordinary way and tightening a minute amount.

Go Easy on this. It Doesnt take much force to spread the slot a lot.

Number 2. The SHOCK trick.

Quite a few parts on a bike have a tendency to “self tighten”, freewheels and pedals are the obvious examples. Others can corrode in place and seem almost impossible to remove. In these circumstances it is essential to have the right tool for the job, rounding off a quarter inch Allen key bolt by using a slightly smaller 6mm allen key (like on an American made stem) is a great way to piss yourself off. But even with the right tool some things can seem immovable. Trying to get a pedal undone is great fun, with all the possibilities it offers for skinning your knuckles or driving a sprocket tooth deep into your arm.

In these cases the seized thread responds much better to a SUDDEN application of torque than it does to a relatively gradual push. So for example in the case of a pedal, position the pedal-spanner in a good position for you to stamp on it, make sure that the spanner is well on the flats then just STAMP on the fucker. The sudden jar will be much more likely to break the pedal free of the crank.

Bear in mind that cheap spanners (and even some supposedly good ones) might not take this kind of treatment too well and could conceivably snap so be careful, read all warnings on tools, wear eye protection, stick a helmet on etc etc….

IF you are going to use this trick, make DAMN sure that you are going to turn the spanner the right way, if you do this the wrong way and tighten it in even more it isn’t going to help much. Remember that left hand pedals have a left hand thread so undo clockwise. Most other threads are right hand and undo anti-clockwise…

If the crank is already off the bike then you can put the spanner on, then prop the spanner-crank-pedal assembly on the ground so it forms a little mound. Provided you have thought it through and propped them the right way up, a good stamp on the top will loosen the pedal off nicely. Note that it is a good idea to think about the floor underneath before doing this. It WILL get ragged.

It is much harder to apply the same kind of shock to a stuck freewheel but if you can it will help. What I do in this case is to make sure the freewheel remover is securely bolted to the wheel with the wheel nut (or bolt) first. Then clamp the remover firmly in a good solid bench vice. With the tyre still on and at least slightly inflated, grip the two sides of the wheel in each hand and brace yourself. Now, instead of the normal “heave”, what I do is wind myself up then scream “Strength of a bear!” and throw my weight in the correct direction as hard as I can, really freak out on it. You will look like a tit, but the chances of breaking the freewheel thread free are much improved and that’s what matters.

Make ABSOLUTELY sure you are going to turn the pedal the correct way before stamping.

The last tech column had a stupid name. It’s not the name that I gave it so please don’t blame me. It was entitled “Truth” originally but for some reason it got changed to “Build Your Own Wheels”, which, although a good idea, was very little to do with the article which was just about truing wheels. This month the column is called “Lard inspired quest for reliability and tranquillity”. If it has been changed then you know it’s not because of me. I don’t think Mark ever proof-reads these articles, I think he just does a “search and replace” on fuck piss shit twat etc so this paragraph should escape editing and you will all know the real title…

So Lard sent me a lovely e-mail all about how “The other day my pedal snapped as I cranked out in front of an Audi TT at a 3 lane roundabout.” So he wanted to know if there were any standard checks you should do before riding your bike. Hmmmmm…..

Well yes. But I really want to talk a bit about how things break before I mention them. Unfortunately Lard made it pretty clear that I waffle on like a dick way too much in these columns so he isn’t going to be too pleased about it if I do. Look away now Lard.

I just can’t see how I can talk about avoiding part failure without talking about how things fail. Failures basically fall into two categories which I will call “catastrophic” and “progressive”. In Lards example his pedal spindle snapped clean off as he accelerated. This usually causes you to throw yourself over the bars under the approaching bath tu- , sorry Audi TT and could safely be called catastrophic. One minute the pedal was doing its job fine, holding up Lard’s manly figure and transmitting all the power of his lithe young legs to the cranks, the next moment, complete breakage. So what changed?

A pedal axle is usually steel, and in the case of a “loose ball” pedal (ie. One that doesn’t use cartridge bearings) it has to be at least surface hardened to resist the wear of the balls. As steel gets harder it generally gets stronger but you never get owt for nowt so it also gets more brittle. In a low temper, steel may start to yield or stretch and bend at a stress of say 400 Newtons per square millimeter, as we increase the hardness of the steel its strength may increase to over 1000 Newtons per square millimeter. The downside is that while the low temper steel would stretch and bend a lot making it obvious that it is breaking, the harder material will barely move and give little sign of anything being wrong right up to the point where it suddenly snaps. This is the dilemma that faces every engineer using almost any material to make bike parts. For safety’s sake he wants the part to make it obvious that something is going wrong before it breaks but on the other hand he wants it to be as strong and light as possible.

To complicate matters he can do a lot of fancy juggling with the tempers and hardnesses of the component. He can harden the surface of a component like an axle so that the outer layers, that have to deal with bearing wear, are much harder than the inner core of the axle. A typical pedal axle is therefore “case hardened” with a tempered core which is more resilient.

So what happened to Lard? Did he simply pedal so damn hard that the pedal snapped off in one go? Perfect then snapped in a fraction of a second? Probably not. The likely explanation is that the pedal had been slowly breaking for sometime. My guess would be that Lard had had his pedals a while and that they bent almost as soon as he fitted them. I am sure that we have all experienced the feeling of riding someone else’s bike and thinking that the pedals and cranks are bent. The reason for this may be that they are; or that yours are and you are used to it, so straight “feels” bent; or most likely both sets are but in a slightly different way.

What I would guess happened is that a while ago, Lard bent his pedal, at which time the brittle outer “case” cracked through and the tempered inner core bent slightly. But it didn’t break completely because the movement of the inner core absorbed the energy of the impact. Since then repeated impacts will have made this small crack grow slowly across the pedal, maybe repeated impacts slightly work hardened the axle as well.

Over time a tiny crack opened up across the pedal, then on that fateful day it was so weakened by the crack that Lard’s explosive accelerative effort snapped it clean through the last part and dumped him on his head in the street. If Lard had gone back and looked at his snapped pedal spindle he probably would have seen that the broken cross-section of axle had two distinctly different surfaces. A smooth flat surface where the crack had been slowly growing and a rough crystalline looking surface where it finally broke. The crack might only have been small, maybe just a tenth or a twentieth of the way across but that is the crucial stage.

So now we know how and why it broke how can we catch it before it happens again? Well the key is to identify the time when it first bends and replace it then. This is easy enough to do, just remove the pedal from the crank and spin the axle in the body. If the end of the axle “wobbles” as it turns (and the bearings aren’t loose) then you know the axle is bent. Unfortunately most pedals seem to bend slightly within a few rides yet are quite capable of lasting years before the crack grows large enough for them to snap. We have very little option but to hope they need replacing for some other reason before then or just wait to slam your knees into the bars…

The really worrying one is forks. If your forks snap you really know it, the chances are it will happen on a big jump or other hard landing and you will already be heading towards the ground with some speed. At an approach speed of say 30mph if the forks break you probably have less than a tenth of a second from the point they break to your face hitting the ground (or your bars), no time to prepare for the slam of your life. Luckily forks do not need a hardened bearing surface for the headset (because there is a separate race) so they do not need to be surface hardened, crack development is much less likely and being a big hollow tube it is much more likely to bend before it cracks. But if you ignore a bend it will crack eventually. Never risk it with forks, if they are bent replace them immediately!

It should be fairly easy to spot a bent fork, they nearly always bend on the steerer tube just above the bottom headset race so any bend is obvious just by looking at the bottom headset parts. You don’t need to take anything apart to do it just look at the bottom of the headset from the side. If the bottom of the fork crown is not perfectly parallel to the bottom cup then chances are the forks are bent.

Cranks are another case where fatigue will be the big worry. Small cracks will develop and grow slowly then faster across the arm until it is ready to snap all the way. These will usually start on or near a weld so keep an eye out for them. If you see them then you can usually weld them back up fairly safely but if you ignore them they will eventually snap under you.

I am not suggesting that you should get down on your hands and knees after every trick and examine every inch of your bike with a magnifying glass for cracks, but if you have a little look round now and again it may save you some pain down the line.

There is one other thing that can help a lot, noise. As a crack grows it will often make a clicking noise or a creak or groan. If your bike makes any funny noises keep an ear out for more. I once had an Auburn race frame which I rode steeet on. At one years KOC I noticed it was making a really annoying click every time I cranked hard on the pedals. Sprinting at the pyramid banks it would go click click click on every pedal stroke. Later that day I tried to find the cause, I started looking the bike over and wobbling things. Is the headset tight? Check! Back end bolted on tight? Check! Pedals and cranks tight? Check! Stem tight? Check! Massive crack in downtube? Check! Ah. That might be something to do with it I suppose… The crack was three quarters of the way round the downtube and open a good three millimeters at the bottom, one more big impact and I probably would have torn the headtube clean off, with the inevitable injuries.