Technical FAQ: More about stopping high-speed shimmy

Have a question for Lennard? Please email him at veloqna@comcast.net to be included in Technical FAQ.

Dear Lennard,
I read your post regarding high-speed shimmy, and you suggested weighting one wheel, the back, or clamping knees to the bar. I once had a situation at 100kph. To make a long story short, the bike became completely uncontrollable, and because of the slope towards the ditch, it went in that direction, I couldn’t steer it. I didn’t know what to do, and there were a lot of riders behind me. As I was about to enter the ditch, I did one of those panic maneuvers by unclipping on one side, standing up on one pedal and lowering my crotch toward the bar. Guess what happened – the bike immediately regained equilibrium. So, when I put all my weight into the front end, it stopped the wobble. I swerved away from the ditch, and I’m still alive to tell the tale. Clamping knees to the bar would not have helped, that’s for sure. I could barely hang on to the bars. So, I would recommend getting into the front end with all your weight as a way to stop it.
— Neil

Dear Neil,
I’m glad that worked. Yes, for the same reason that getting as much of your weight as possible on the rear wheel can stop a shimmy, shifting your weight over the front wheel can have the same effect. Thanks for pointing that out.
― Lennard

Dear Lennard,
I just wanted to add one more possible reason for high-speed shimmy, and it’s something that I experienced firsthand. I had a base model Cervélo S5. From my first ride, I had shimmy, and it was scary. After years of dealing with it, I finally contacted Cervélo, because my R3 was solid going downhill, and I showed them a picture of what I had been told was just a cracked clear coat. Turns out the top tube was cracked, and that’s what was causing the shimmy.

So that reader’s friend may want to have the frame checked, even if it is new; it’s possible something could be wrong with it.
— Chris

Dear Chris,
Very good point. A cracked frame, fork, or rim could all lead to shimmy problems.
― Lennard

Dear Lennard,
Your recent answer to the solution for steading high-speed shimmy in the VeloNews column is the same as mine: Unload the front wheel by moving as far to the rear as possible with the chest on top of the saddle. This stops shimmy reliably as might other techniques you mentioned.

Wheel characteristics come into play as a source as you will find in A. Sharp’s book of 1898, depicted directly below in an MIT reprint, page 352, the second picture.

In Fig. 355, 5 arrows are depicted sequentially showing the lateral forces on the rim of a conventionally laced wheel. Numbering the arrows 1 through 5, left to right it becomes obvious that if spoke 3 is a bottom pointing spoke and become slack during rotation under load its lateral force component (pointing down) disappears and the adjoining spokes, No. 2 & 4 continue to assert their lateral force (pointing up). Spoke 3 can no longer laterally balance spokes 2 & 4 and the rim unavoidably moves out of the center in directions 2 and 4. This phenomenon, alternating left & right as alternating spokes get unloaded the under load during wheel rotation can set off shimmy. At high speed, this can become completely uncontrollable and extremely dangerous. It has happened to me with conventional wheels and I’m lucky to have survived. I stopped the shimmy by exactly applying your solution by totally unloading the front wheel.

Now consider my solution to this. If we move the spoke attachment points exactly opposite each other on the rim, as in my patented paired spoke lacing design, all the lateral alternating forces neutralize each other and can no longer pull the rim out of the wheel center plane. Thus, the lateral force vector of spoke 1 & 2 disappears as do those of spoke 3 & 4 and so on around the rim during rotation under load.

This solution is especially important in low spoke-count wheels and demonstrates why years ago Campagnolo’s conventionally laced 12-spoke was quickly withdrawn from the market. I’m currently riding 10 and 12-spoke wheels with my design and consider them the world’s fastest. These wheels sit comfortably at .009 inches in hop and .007 inches in wobble without maintenance for thousands of miles, depicted in the third picture below.

This analysis of paired spoking along with my previously explained advantages which you graciously published in VeloNews should persuade those who continue to believe my intent was purely aesthetic.

Thanks again for the on-point analysis of shimmy.
— Rolf Dietrich, founder Rolf Wheels and Rolf Prima

Dear Rolf,
Thanks for pointing that out. We build all of the wheels for the bikes we make for really heavy and tall riders, and we always build them with 36 spokes. The heavier the rider and the taller the bike, the greater the potential for high-speed shimmy. Super-stiff wheels reduce this potential, and, while they are not paired spokes as you describe, the fact that there are so many spokes means that the distance between spoke nipples is small, so the amount the rim moves back and forth on the ground as the bottom spoke is de-tensioned by the rider’s weight is minimized.
― Lennard

Dear Lennard,
I’ve just read your tech FAQ column, and I can add my 2 cents on the Campy question Robert asked.

For the last three to four years, I’ve been running a Wolf Tooth Road Link adapter on my Campy setup, and it works great.

First, I’ve used it with a 10-speed Chorus short cage derailleur (coupled with 2016, 11-speed Super Record Ergopower levers), the cassette was all along SRAM PG1170, 11-36. This setup worked like charm.

About a year later, I upgraded to regular 2016, 11-speed Record rear derailleur, and it still works just fine (it seems as if 10-speed Chorus was shifting a bit quicker, but hardly a noticeable difference).

Up front, I’ve been mixing pure Campy 53/39 and 52/36 hybrid (Campy cranks and O-Symmetric rings).

I’ve been using 110-link Campy chains, and that’s it (at some point I tried a SRAM Red chain; it worked nicely, but it didn’t last nearly as long as Campy does — about half the distance I’m getting from Campy).

Everything is working just fine, and I guess I can go up to 40 at the back (as per Wolf Tooth website, but I haven’t tried that so far).

All Robert needs, besides a bigger cassette, is a Road Link by Wolf Tooth and a longer chain.
— Krako

Dear Lennard,
Re: Effects of temperature and time on tire pressure:

From the ideal gas law one can predict the relationship between pressure and temperature for a fixed volume: P₂ = P₁ * (T₂/_T1)

P₁ and T₁ would be the pressure and (absolute) temperature at one time, and P₂ and T₂ would be them at a different time.

If temperature 1 is 60F degrees  (289K) and temperature 2 is 90F degrees (305K), then this predicts P₂ = P₁ * (305/289) = 1.06 * P₁.

This predicts that the tire pressure would increase by 6 percent as the temperature heats up from 60F to 90F.
— Raymond

Dear Raymond,
Thanks for that theoretical analysis. It is more consistent with Specialized’s measured results than it is with Jack’s fears that the increase in tire pressure with increasing temperature on a ride “must be astronomical.”
― Lennard

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn on Twitter.