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Discussion Starter #1
Is there any reason to think a longer versus a shorter stem will cause or cure a shimmy??

I know what causes a shimmy is the harmonics of the frame, etc. and that clamping the top tube is much of the fix when it happens. I can make a case in my head that longer would be more stable, but having the weight further forward might be a negative to offset it. Any wisdom out there would be appreciated.

I'm trying to overcome a very, very bad experience with a shimmy. I hit a stone and that began a terrifying ride until I got it under control which seemed to take forever. I know it's an issue in my head now when descending, but it is still an issue, so I'm looking for some confidience building advice.
 

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pinoy thunder
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I can tell you that when I switched to a longer stem (100-120mm), my bike felt more stable on descents. Maybe it was something to do with my position on the bike. I don't know if this applies to you though..
 

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No..

I assume you're riding a fairly large size frame? Most who report shimmy ride a large frame that's more prone to flex and/or they are on the heavy side. A flexy fork might also contribute to the problem.

There might be some small chance that increasing the weight on the front might help, but a longer stem will not do that. Your whole body would need to move forward, so moving the saddle forward along with a longer stem (just to restore your reach) would be required to make any significant difference.
 

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Discussion Starter #4
Not Large Frame or Body

Actually, I am riding a Trek 5500, 56 frame size and am 5' 10" tall. My weight is about 146 pounds.
 

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pinoy thunder
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C-40 said:
I assume you're riding a fairly large size frame? Most who report shimmy ride a large frame that's more prone to flex and/or they are on the heavy side. A flexy fork might also contribute to the problem.

There might be some small chance that increasing the weight on the front might help, but a longer stem will not do that. Your whole body would need to move forward, so moving the saddle forward along with a longer stem (just to restore your reach) would be required to make any significant difference.
I forgot to say that I switched to a no setback post as well.:eek:

A guy in my club returned his carbon Scattante to Performance after experiencing a shimmy.
 

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Steaming piles of opinion
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msohio said:
Is there any reason to think a longer versus a shorter stem will cause or cure a shimmy??
I think it's a wrongly formed question. Stem length should be changed for issues of fit, and no other reason. Assuming the bike fits correctly now, changing the stem will reduce shimmy, because you'll end up uncomfortable and so ride less.

Pontificating aside, a longer stem will increase the sense of stability. But steering stability isn't the same as shimmy prevention. My gut says that it also would increase the opportunity for shimmy, because it adds additional elastic tension to the system both in terms of musculature and the longer moment of the components. In my experience, shimmy is easier to dampen from the tops vs the hoods, and a longer stem is an extension of that concept.
 

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check a few things...

msohio said:
Actually, I am riding a Trek 5500, 56 frame size and am 5' 10" tall. My weight is about 146 pounds.
I'd check the wheel bearings and headset for excessive play. Also be sure your spokes are properly tensioned. Frame alignment could be off, but it probably can't be corrected, unless a little filing of the fork tips or rear dropouts would do it.

Other than that, I'd guess this is a freak occurence. If the rock you hit was big enough to turn the front wheel, your shimmy may have been unavoidable. Sometimes it's the rider's paniced response that makes it worse. I've never experienced shimmy, so I can't provide a lot of good advice on how to respond.
 

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May be a freak thing that won't happen again any time soon. That doesn't help does it?

The nice thing about shimmy is that the wheels are ussually spinning fast enough to keep you upright. I agree with danl1 and c40 stem is for fit although I like 120mm stems in order to keep my hands more over the front axle. Trek may have improved the resonance of the5500 as I know that bike goes back a ways. I was descending with a freind on an older 5500 Saturday and he seemed tentative. Maybe he's been bit by the same dog.
 

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In my case, my Giant TCR will shimmy from time to time at high speeds. I now grap the top bar with my knees on fast descents and that seems to cure it. It has the added benefit of taking weight off my bars and letting me have "light hands", which are both good things to reduce a shimmy. My shimmying is usually at 40MPH or higher. I had a bad one occur as I approached 50MPH (before I learned the grip the top bar trick) on a long downhill. No longer go that fast down that particular hill.
 
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