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Discussion Starter #1
have a question about the above. i've been riding a mtn bike for 3 years. got a Litespeed Teramo last Nov and rode it on a trainer all winter. have been out on the roads 4 times so far. it's nice and stable most of the time, including coasting downhill up to 40+. i notice a 'shimmy' however when i'm pedaling fast at that transition point at the bottom of a downhill going to flat or starting back up. i'm 5'10" and 200lbs. not fat but would like to lose a few.

i'm thinking this is related to a less than perfect pedal stroke. likely? is this usual?

also, i've got neuvation aero wheels on it and i noticed some shimmy in a strong crosswind last time i was out. i've heard aero wheels are susceptible to crosswind affects but not sure what those affects would be. is shimmy one of them?

thanks for any and all help
 

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Shimmy, wobble, or instability?

daverk said:
have a question about the above. i've been riding a mtn bike for 3 years. got a Litespeed Teramo last Nov and rode it on a trainer all winter. have been out on the roads 4 times so far. it's nice and stable most of the time, including coasting downhill up to 40+. i notice a 'shimmy' however when i'm pedaling fast at that transition point at the bottom of a downhill going to flat or starting back up. i'm 5'10" and 200lbs. not fat but would like to lose a few.

i'm thinking this is related to a less than perfect pedal stroke. likely? is this usual?
Is this a true shimmy, or just a wobble? A shimmy is an oscillation that feels as if the front of the bike is being shaken by some force, whereas a wobble is more like a side to side steering motion. Does the bike bike shimmy/wobble if you don't pedal in the transition? Does it stop if you stop pedaling? If so, then it is probably not a true shimmy, and the bike is probably wobbling due to a unbalanced pedaling. I assume that your cadence (pedaling RPMs) are quite high in this zone? Many people's pedaling smoothness falls apart at high RPMs, and can produce a lateral component that wobbles the bike.


daverk said:
also, i've got neuvation aero wheels on it and i noticed some shimmy in a strong crosswind last time i was out. i've heard aero wheels are susceptible to crosswind affects but not sure what those affects would be. is shimmy one of them?
If a bike is prone to shimmying, than at the right speeds a crosswind can set it off. But if a bike is not prone to shimmying, it won't start just because of a crosswind. And not all instabilities are shimmies - a crosswind can certainly make a bike's handling unstable, but a shimmy is a speed related resonance that may continue or even grow after the initiater is removed.

More typically, wind acting on the the larger side-profile of deep section rims can create steering torques which can make steering erratic and more difficult to control.
 

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Discussion Starter #5
your premise fits the evidence

i think you're right. the 'whatever you call it' does settle down if i stop pedaling. and it is primarily at high cadence. i find it a little unnerving but not as scarey as a high speed shimmy would be. guess i better just keep working on my stroke. thanks
 

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Sounds like it has to do with your pedal stroke

I'm still having trouble trying to visualize your problem. Whatever it is, is is apparently related to your pedal motion.

As others have noted, make sure your saddle height is adjusted properly. To help smooth your pedal stroke, do some one-legged intervals (pedal with one leg at a time for 30 or 60 seconds each interval, trying to keep the revolutions as smooth as possible) and then regular two-legged fast-spin intervals (spin at as high a cadence as possible >120 rpm without bouncing on your seat for 1 or 2 minutes per interval).

Another thing that I have found helpful is pedaling on a trainer and listening to the "whirr" noise that the trainer makes. If it goes "whirr whirr whirr whirr whirr whirr" as you pedal, you aren't being smooth. Try to get it to one smooth, constant "whirrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr" and notice what that smoother stroke feels like.

And whatever you do, make sure you keep your knees in close to your toptube when you pedal, or at the very least, keep them in line with your feet and hips. Not only does nothing looks uglier than bowlegged pedaling with knees sticking out to the side, but it costs you in smoothness and performance also.
 

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Discussion Starter #8
on the trainer i can go a bit over 120 before i start bouncing. this is happening around 100. of course, i know it's different on the road.
 

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I've seen riders who see-saw their handlebar at high cadences. On the left downstroke, their left hand pulls the handlebar back a fraction. On the right downstroke, the right hand pulls back. Sometimes you even see someone pull at the diagonal.

To see if you're doing this, forcefully push both hands into the curved part of drops for a few seconds when pedaling at a high cadence. If the oscillation stops, your hands responding to the movements of your legs could well have been the problem.

Because it takes more force to rotate the handlebar on a stationary bike, trainers tend to mask this problem. Rollers, on the other hand, would make it apparent immediately.
 

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Because it takes more force to rotate the handlebar on a stationary bike, trainers tend to mask this problem. Rollers, on the other hand, would make it apparent immediately.
Yeah. And it'll instantly make you hit the floor too. :) Good advice though.
 

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Yeah. And it'll instantly make you hit the floor too. :) Good advice though.
I hereby nominate you for the title of RBR Archaeologist of the Month. :thumbsup:
 

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I'm still having trouble trying to visualize your problem. Whatever it is, is is apparently related to your pedal motion.

As others have noted, make sure your saddle height is adjusted properly. To help smooth your pedal stroke, do some one-legged intervals (pedal with one leg at a time for 30 or 60 seconds each interval, trying to keep the revolutions as smooth as possible) and then regular two-legged fast-spin intervals (spin at as high a cadence as possible >120 rpm without bouncing on your seat for 1 or 2 minutes per interval).

Another thing that I have found helpful is pedaling on a trainer and listening to the "whirr" noise that the trainer makes. If it goes "whirr whirr whirr whirr whirr whirr" as you pedal, you aren't being smooth. Try to get it to one smooth, constant "whirrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr" and notice what that smoother stroke feels like.

And whatever you do, make sure you keep your knees in close to your toptube when you pedal, or at the very least, keep them in line with your feet and hips. Not only does nothing looks uglier than bowlegged pedaling with knees sticking out to the side, but it costs you in smoothness and performance also.
Another trick to pedalling smoothly at higher cadences is to imagine yourself spinning smaller and smaller circles with your feet.
 
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