Bicycle Alignment

1. Make certain BOTH front and rear wheels are properly dished.
2. Make certain dropouts are properly aligned.
3. Do a quick frame alignment check - string test and ruler should be good enough.

^ That will eliminate "pull" as a cause and YOUR reaction as a feed and continuance.


Geometry

As already noted, bikes with very aggressive fork rake tend to be prone - usually in old school days what we call "crit" or "track" bikes. They ride on rails, awesome in corners with very responsive handling at pedaling speeds.


Baggage

1. If carrying front end baggage, try to keep the center of that weight behind the front wheel axle.
2. Any baggage carried on the back end, try to keep the center of the weight forward of the rear axle.

Otherwise, any input they provide movement wise has a delay input wise hence the oscillation effect.


Positioning

1. Knees against top tube.
2. Heels against chainstays - if you're comfortable with that.
3. Shifting weight forward or back a little.

About handlebar grip...

I'm glad someone brought this one up. It is actually worth testing as an option. A master framebuilder in this area makes a "truck" bike. It has a shimmy. He said, "Don't grip your bars like a madman, relax."

Sure enough, the shimmy went away immediately. Sometimes, by going stiff or locked in your grip, all you are doing is acting as a base for rebounding.

So it's worth testing when troubleshooting a shimmy.


I've actually had the scary luxury of getting into the high 50s, low 60s speed wise on a downhill - only because a storm had moved in and the wind was going downhill assisting me. Normally, it'd be in the 40s speed wise. All my bikes have been road bike with relaxed front ends or decent fork rake, so I haven't really had to deal with the problem.

Benotto 2000, Lotus, Raleigh Competition, Tommasini Sintesi.

=8-)