Originally Posted by
blakcloud
Today I experienced a shimmy that I couldn't control. I went for a ride today and twenty minutes in I was descending a hill at 56 km and then in no time I am skidding along the pavement. The shimmy turned into a full out wobble that I just couldn't get under control.
Two weeks ago I experienced shimmy at 82 km an hour and I was able to slow the bike down and control it. I had a smaller one a few days ago at about 70 km/h. Today's was much slower but I had hit some rough pavement that may have contributed to the wobble.
Did I help contribute to this mishap, you bet I did. I didn't grab the top tube between my legs, I didn't raise my weight above the saddle or loosen my grip on the bars. These are all solutions but they are counter-intuitive when it is happening. I was hanging on for dear life, just trying to slow the bike down. I think I need to start training for this to make sure it doesn't happen again. I have done a lot of reading on speed wobble and one thing is clear, there is no definitive answer. Different solutions work for different people and the solutions are not universal. My biggest obstacle will be fear. The fear to go downhill fast again.
This is just a narrative of what happened. I was one of the unlucky ones that couldn't control today's shimmy.
The bike was the Trek Domane SL6 that is one year old exactly today.
(bold) As an experienced rider and an engineer, I agree with clamping around the top tube, although if seated, that should not be necessary assuming a seat post with greater rigidity than a wet noodle. But raising your weight above the saddle, if you mean torso, fine, but I would think you want to stay seated in the saddle to increase the lateral rigidity and mass damping of the system, to slow down the oscillations. My bike is touchy, it's a 20" wheel folder, and I have a firm grip on descents, and control my speed, I don't sail down the mountain like I used to on my Cannondale criterium racing frame. Even if it had more trail to the fork, I think with the reduced rotational inertia of the wheels, there's no way it would have the stability of a larger bike on fast descents. On the Cannondale, I've topped out the speedometer and I think it maxed at 65 kph if I recall correctly, that was 20 years ago.