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Help with Wobbly front end!(4 posts)

Help with Wobbly front end!regulajo
Sep 14, 2002 11:33 AM
Riding down a steep canyon yesterday, lightly on the brakes to control speed, bike starts to shimmy or wobble very badly mostly in the front end it feels like. Going only between 35-40 MPH with some crosswinds. I'm riding a 2002 Specialized Allez Pro with Mavic Ksyrium Elite wheels. Years ago I had ridden bikes much faster and never had this problem. Anyway, it was very scary and I'm wondering what might cause this? Thanks, Steve
Speed wobbleKerry
Sep 14, 2002 12:20 PM
It's not quite clear from your description if the front end shimmy took place during braking or after you let off the brakes or was triggered by the braking but continued after. One place to look would be a loose head set, if the wobble happened while you were braking. Otherwise, you are looking at a phenomenon largely caused by a frame that is not stiff enough in the region of the head tube and top tube. The whole bike/rider system is involved, and often things like changes in rider position, adjustment of the head set or wheel bearings, different tires (maybe even tire pressure) can change the resonant frequency so that it doesn't happen. The immediate solution is to clamp your knees on the top tube - this stiffens the top tube and changes the resonance.
Speed wobbleregulajo
Sep 14, 2002 12:56 PM
The wobbling began during braking and continued after. This happened before when I first got the bike (used) and the headset was a little tight. I had the headset adjusted by my LBS. I have ridden at higher speeds on this bike since adjustment and not had the wobble. So I wonder about the combination of crosswind/Rider size/compact lightweight frame? I am 6'1" 180, riding the 61 cm bike.
Frame sizeKerry
Sep 14, 2002 1:15 PM
Larger frames are more prone to speed wobble because they are more flexible. All factors enter into it - sometimes you can predictably get speed wobble, and other times it seems to come and go. If the problem repeats, you're looking at the frame being too flexy. Compact design would have little to do with it inherently.