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Old 10-22-12, 08:19 PM   #1
Ron47
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Front wobble on a Trek 520

Hello everyone...I have a Trek 520 touring rig that I built up from a mid 90's (I think) era 520 frame, with a 1" threaded steerer and the stock 520 fork. I run Velocity Dyad rims and 700 x 35 tires. It has never been wrecked. It has never been loaded for touring, and I use it as my primary commuter. I've noticed that, if I take my hands off the bars when I ride, there is a pretty substantial front end shimmy. It happens at pretty much any speed, though it does get worse the faster I go.

Prior to this I had Mavic rims on the bike, and still had the wobble.

Any suggestions on what may be causing this?
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Old 10-22-12, 08:25 PM   #2
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There could be several culprits:
- Check head set tightness.
- Check the tightness of the front wheel bearings. This one got me for a long time before I figured out what was happening.
- If it is a large frame,e.g., 60cm or larger it might be inherent in the frame. When the oscillation starts press your knee against the top tube as a damper.
- Check the "trueness" of your wheels.

Good luck.

Last edited by Doug64; 10-22-12 at 10:57 PM.
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Old 10-23-12, 10:13 AM   #3
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Assuming that there isn't anything mechanically wrong (like a loose headset, sloppy axle bearings, loose spokes or something like that), shimmy can have a ton of causes- it can happen at a certain weight distribution with certain geometries and at certain speeds and certain frame and wheel flexibility. It's dangerous and scary. The Trek 520 was optimized for loaded touring, weight on the front and back. Eliminating unloaded shimmy when riding hands-free was probably not high on the design criteria. That being said- to get rid of your shimmy, the best thing to do is to not ride hands-free. When you do ride hands-free, hold your thigh against the top tube- that will damp the oscillation. If you really want to get rid of it, changing the fork to one with a lower rake will help- increases trail and adds stability at the cost of making the bike handle worse with a front load. A good 10 mm less fork rake will change things considerably.
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Old 10-23-12, 04:21 PM   #4
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This may sound crazy, but I had a bad wobble. When I removed the tire liners from my tires the wobble went away. The liners kept the tires from taking the shape that the tires should have when inflated.
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Old 10-23-12, 04:48 PM   #5
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Yeah, could be the tires. Try a new tire up there. To damp a shimmy, squeeze the top tube hard between your knees, move forward slightly to put more weight on your hands and put the rest of your weight in the pedals. Plus relax your grip. These suggestions are for a bad shimmy when descending, which is when it usually happens.
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Old 10-23-12, 05:30 PM   #6
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Assuming the shimmy only happens when you sit up and ride with no hands, then it may well be that you have too much weight too far back on the bike. Does it still happen when you remove all baggage?
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Old 10-29-12, 10:05 AM   #7
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Hi everyone, and thanks for the suggestions. I've checked the suggested fixes, but so far nothing. Headset is good, tires were swapped for another set, hubs are good, etc. Fortunately it only happens if my hands are off the bars; when I'm holding them, even in a fast descent, there is no shimmy. I may try lengthening the derailleur cable housings on the front; the loops seem a little tight, and maybe they are putting uneven pressure on the forks.
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