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Stopping high speed wobble(4 posts)

Stopping high speed wobbleKen of Fresno
Jul 3, 2003 1:18 PM
Just read this from the RBR newsletter and thought it might be interesting to some here:

One FAQ at RBR is what causes a bike to shimmy on descents.
More important, what can be done when a bike is shaking at
the edge of control?

After his recent talk at Ride the Rockies, Fred was asked
this question along with Ron Kiefel, the former Tour de
France rider who owns Wheat Ridge Cyclery in Denver.

Ron offered some advice that Fred hadn't heard before. It's
based on his experience hurtling down switchbacked roads
in the Alps and Rockies.

Bikes generally begin to shimmy when the rider is in the
standard descending position -- crankarms horizontal, weight
distributed among hands, feet and seat. Shimmy almost never
begins when the bike is laid over, as in cornering.

Therefore, Ron says the way to stop a developing shimmy is
to drop one pedal (as if you were about to go around a
corner) and press your weight on it. This lowers your center
of gravity and changes the vibration characteristics of the
frame, thus reducing its tendency to shake.

Ron's tactic might be best on a compact frame, which because
of its low, sloping top tube prevents another effective
shimmy stopper -- squeezing the top tube between your knees.

Here's another trick: Get in the habit of descending with a
knee (or calf) resting against the top tube. This can damp
shimmy before it ever begins.

For more on causes and solutions, plug the words shimmy and
wobble into our site search at www.RoadBikeRider.com

Ken
I've used the knee on the top tube trick for decades ...Humma Hah
Jul 3, 2003 1:26 PM
... that's how I wore the paint off the top tube TWICE. So thanks for the pedal-down trick ... it might save my expensive decals and powdercoat.
Dropped pedal - Works on Bianchi EV2 (nm)Iwannapodiumgirl
Jul 3, 2003 3:48 PM
Ummm.....not quite.....Alexx
Jul 4, 2003 11:43 AM
"Therefore, Ron says the way to stop a developing shimmy is
to drop one pedal (as if you were about to go around a
corner) and press your weight on it. This lowers your center of gravity and changes the vibration characteristics of the frame, thus reducing its tendency to shake."

Yes, it will change the vibration characteristic of the bike, but unless you unclip your other foot and nearly drag the pavement with it, you will NOT lower your center of gravity. Likewise, simply putting force on the lower pedal will change the vibration characteristic, but not from changing the center of gravity. In both cases, your center of gravity will remain the same (or very nearly so).

From my experience, a person should first make sure that their elbows are bent, and secondly that the hands aren't giving the bars a "death grip".