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I have a Gary Fisher Kaitai, their low-end hybrid. I use the bike for commuting so I have a rear rack and typically carry between 5 and 12 lbs back there. When I get up to moderate speed (10-15mph) and let go of the bars they begin to wobble badly. This happens to a lesser degree when there is no load on the rear rack, as well. The wheels are true and balanced, and I am riding Bontrager 700X32 road tires.

Is it possible to correct this?

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1 Answer

up vote 2 down vote accepted

There are a few things that could help the shimmy, but there is no real silver bullet.

Typically the shimmy is a function of head tube angle, top tube length and frame (specifically top and down tube) elasticity. Jobst Brandt describes it best in this article so I won't get into too much detail on the whys. There are a few things that reduce or negate the shimmy that have worked to varying degrees for myself.

1) Knees against the top tube. Squeeze the top tube with your knees. 2) Stem length. Sometimes a longer stem might help out. Very frame dependent and you would not want to change your fit imo. 3) Handlebar bag. Distribute some weight to the front and see if a handlebar bag can help overcome the gyroscopic forces created by the wheel. 4) Switching to a set of tyres w/ more 'tread' (ie. knobbies). I haven't tried this but the jobst brandt article indicates this could work.

The Kaitai is pretty unique in its long top tube, exceedingly short head tube and relatively steep head angle. This also makes the bike a 'tough fit' for the majority of people.

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I was about to spend a bit of cash on some rear panniers, so thanks for the advice. Am I asking too much to expect my $600 bike not to behave this way? –  Tom Stephens Oct 4 '10 at 14:46
    
I can't say for sure without seeing the actual bike itself. I would suggest trying a few of the lesser expensive 'fixes' and seeing how it goes. I have ridden the Kaitai and not experienced the shimmy ... so I would assume it isn't across the board. As well ... and I forgot to ask this, does the bike do the 'shimmy' w/out any weight on the back end? –  tplunket Oct 4 '10 at 20:25
    
Yes, the shimmy happens without the weight, but is far less severe. –  Tom Stephens Oct 4 '10 at 21:16
    
Have you had someone else ride it, to similar results? If so I would keep w/ recommending you put a handlebar bag on the front ... something to give weight to the front end. Again ... these are all recommendations w/out seeing the bike so please, take it with a grain of salt. Loose headset? Quick release? Hubs? Mis-aligned dropouts? –  tplunket Oct 4 '10 at 22:04
    
Thanks for all of your great suggestions! I am working with my lbs where I purchased it but they are an hour's ride away and I've been awfully busy recently. –  Tom Stephens Oct 4 '10 at 23:21
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