We have some more Twombolt crank sizes and variations in stock. You can now get them in 180mm and 170mm lengths, in either LHD or RHD. Contact your local shops or mail-orders to get a pair. More photos and information can be found after the link, along with some physics questions…

In our Dailyword archive, you can download the PDF manual and even watch a video how-to of installing these cranks.

From the Catalog:
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Twombolt. Yes, we’re obviously aware that one-bolt configurations and two-piece cranks have been done before. However, what HASN’T been done before is the Twombolt’s unique wedge cluster. This cluster is the heart of the system, and it addresses all of the issues found on ordinary cranks. Now you can finally say goodbye to the “ankle-biting”, bolt-loaded chunks of aluminum and steel found on pinch bolt cranks. Better yet, The Twombolts will also let you bid a not-so-fond farewell to the difficult installations and seemingly endless loosening and “wobble” issues found on archaic spline designs.

The Twombolt’s integrated, ultra-hollow 22 mm spindle is nearly 17% stronger than 19 mm versions, while also managing to save a significant amount of weight. This weight saving helps to put the Twombolt in the same category as three-piece cranks that rely on weaker, expensive Titanum spindles.

The Twombolt arms (with their integrated hex-end spindle) are a 41-Thermal processed assembly, so their strength is backed by a legacy of products with a proven track record for reliability. Guaranteed for life against bending and breaking (as usual). Patents pending worldwide.

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Here’s the physics questions: Based on the simple lever diagrams above, which classification(s) does a BMX crank fall into? And, more importantly, which length (180mm or 170mm) would potentially help you generate the speed needed to jump the Austin Church Gap?

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.

Here are a couple wallpapers floating around that you guys might be into.

The sprocket image has been up as the ad-spot on our MySpace page for a while now and we recently got some inquiries about it. It’s a modified version of page 10 in our 2009 catalog. In it are the Vermont and Million Dollar Sprockets attached to Twombolt crank arms.

You can catch more info about these products on the flipside or by walking to the other side of the rainbow… which are lesser known internet euphemisms for click the Read More button.

The Vermont Sprocket:
Called the Vermont sprocket because it looks like a snowflake, some people think we forgot the sprocket bolt hole, and that was the point. Instead of having to work your design around functional holes, work the holes into the design. 5 different sprocket bolt holes, that don’t look like sprocket bolt holes when they are not in use. 7075-T6 aluminum in 23t, 25t, 27t, 28t, 30t and various sizes.
» View it on the main website

The Million Dollar Sprocket (MDS):
This sprocket is a serious piece of machining, and the prototype seemed like it cost an arm and a leg, hence the name. Surprisingly light for how heavy duty it really is. The MDS has a fully integrated guard machined 360 degrees on one side, an optional removable 360 degree guard makes the chain fully protected from both sides. 7075-T6 aluminum and available in 25t, 27t, 28t, and 30t sizes.
» View it on the main website

Twombolt Cranks:
Integrated, ultra-hollow 22mm splindle (17% stronger than 19mm versions). Similar weight as 3-piece cranks with titanium splindles. RHD and LHD ready.
» View it on the main website

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.

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…)