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Undiscovered Cyclist
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Discussion Starter · #1 ·
Had a new experience at the Death Ride. The bike is an IRD Impala made with 853 steel. Frame is in it's fourth summer and has about 9500 miles on it. Shipped the bike out and put handlebars, pedals, front wheel, etc on it before a shakedown cruise of 30 miles up to Blue Lakes on Wed morning. All seemed fine, hit 45 MPH and smooth as silk. However, coming down the east side of Monitor, had a rather unnerving quiver in it somewhere in the bottom third or so of the hill around 35-40MPH or so. Only way I can think to explain it is frame vibration, even though I originally thought somehow the wheels could be heating up. I tried not to ride the brakes, but gain speed, then decelerate, and repeat.The bike has seen 53MPH in training with no problems. It also happened again near the bottom of Carson Canyon before Woodfords. In that instance, had to slow down to 20-25MPH to get it out, and in this case it was bad enough to make me wonder if it might make me go down. Having descended in the rain after the hailstorm, was surprised that it happened again if it was due to friction. Needless to say, on the in between descents there was some trepidation, but all seemed OK between the two incidents.

The LBS owner has no explanation except perhaps road surface and weight distribution and perhaps braking procedure. He thought perhaps it was also due to thin walled tubing, but when a recent carbon fiber frame reported the same thing, he ruled that theory out. He has experienced it himself, many moons ago, and at slower speeds than I hit. His only suggestion was to get a knee or two against the top tube and be aware of weight distribution and breaking techinque. Also, he wagered that had I looked at the frame, it probably would be vibrating - didn't have the presence of mind at the time to do that. I typically hug the top tube with the knees when going down fast, but actually can't recall the techinque used that day being a first timer on the DR. No hills like that in SE PA.

Any thoughts would be helpful and no doubt interesting.
 

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Lots of posts on shimmy--very hard to isolate the cause given the number of variables. I've had bikes made from all materials--some shimmied, some didn't. You might check the fixable things like tire seating, headset, position on bike.
 

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You should check the wheels and headset, but that's nit usually the cause. Shimmy is a resonance between the frame/rider and front wheel. If you get out of the saddle, it will change the resonant frequency just like the frequency of a pendulum changes when you change its length. When I am concerned about shimmy, I descend with one pedal down so that I can get out of the saddle by extending my leg. Works every time.

em
 

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Banned forever.....or not
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It depends on a lot of different things. What tube sizes is the frame made from? Not too many bikes are made with 1" top tubes anymore. 1 1/8" is even going out of style.
Rider weight plays a big factor in shimmy, also. A heavy rider with a skinny tubed bike will see shimmy more often than a light rider on a steel frame with a 1 1/4 or even 1 3/8 top tube.
 

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Resident Curmudgeon
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Clamp both knees tight to the top tube if/when shimmying starts. That usually stops it.
 

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(not a real racer)
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I had a bad shimmy when I got my new roadbike. Took it back to the LBS and they adjusted the headset, which didn't help much. Turned out it was my tire pressure. I was running 120 front and rear and I changed to 110 front and 120 rear. No more shimmy.
 

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I'm workin' on it....
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I'm having the same problem with my Orbea Orca (I have a thread on the Orbea forum right now). Front end shimmy like crazy, feels like the fork, at anything over 35mph. I've tried to address all the weight distribution, braking, and hand pressure possibilities to no avail. The bike has been checked out enough times that I'm confident it's not a mis-adjustment issue with the wheels or headset. The "clamp your knees on the top tube" trick does help, but I still won't take the bike into the mountains. Last time it happened at 40mph on a descent, and I actually thought I might crash. Too scary to risk on the steep stuff again. Not sure what the actual cause is, but if I pin it down, I'll report back.
 

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Logically (and assuming that loose headset, mis-aligned fork, etc are not an issue) the shimmy should be related to any weird tire/tube arrangement. Just like any car wheel has to be aligned by adding small weights where the computer tells you to add them, so it should be with a bike wheel.

So check the rubber and tube. Change both if you continue to have problems, mount very carefully and check visually for any wobbling of the tire when rotating wheel. Even small wobbling would create shimmy at very high speed.
 

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Arginine said:
I'm having the same problem with my Orbea Orca ............... Last time it happened at 40mph on a descent, and I actually thought I might crash. Too scary to risk on the steep stuff again. Not sure what the actual cause is, but if I pin it down, I'll report back.
Why are you still riding this bike? I had two friends with the same model Litespeed and they both had serious shimmy problems. One is currently on a Giant and the other quit riding.:cryin:
 

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passive/aggressive
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I have been lead to believe that even a small mis alignment of the wheel in the drop out can contribute to shimmy. The wheels both want to be in the same plane and you get an oscillation. The one time I had this I stopped and checked the QR's and the rear was both loose and out of alignment in the dropout.

I am super tenuous to head into the hills now as it occurred at 35mph for me and when ever i get near there it freaks me out.

If it happens again I will be getting rid of this bike (litespeed siena for what it is worth).
 

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Colorado Springs, CO
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631 Posts
Check the front bearings / hubs? Wheels need truing?

Also, maybe it's your tires -- worn out or getting there?

If it didn't happen before, what changed to make it happen? Possible bang-up in shipping your bike to the DR start by the luggage troglodytes?

My first spot to loo would be the wheel truing and the bearings. I had a set of bearings fail on a front wheel and it sounded like a coffee grinder when they went (fortunately no crash or wheel seize up). Could be enough play in there with some bad bearings to amplify the oscillating action of stuff running out of alignment at a higher speed.
 

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Undiscovered Cyclist
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76 Posts
Discussion Starter · #16 ·
Wheel shimmy

Thanks all for the thoughts, some interesting ideas out there. By process of elimination, the only thing I can account for that is different is perhaps head set being too tight by a tad, maybe; road surface initiating it; and some how front wheel not being in the QR correctly. Bearings were just redone, had new tires, wheels where trued, I believe all PM work was done as needed, after all this was probably a once in a lifetime trip. When I unpacked the bike I expected to mess with the fork/headset. Turns out that wasn't needed & I attempted to tighten everything back up status quo. On my 30 mile shakedown cruise, all was smooth, hit high speeds, and no issues. Figured all is good to go. Trying to recall the shimmy moment, I believe my initial sense was a rough road, but who knows? If that is the case, should others have experienced it? I checked the front QR at Topaz, seemed OK, but re-did it anyway. Don't recall any issues on Ebbett's. Perhaps one of those life's mysteries to remain unknown. Maybe the troglodytes?

However, having experienced it once (twice) hopefully I'll be more attentive to all conditions and factors that could enter in should it ever happen again and I won't be so doggone tired next time to process it. Once again, thanks to one and all for input, links, etc.
 

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TWD
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603 Posts
a search on this forum or google for "speed wobble" will give you this info again and more. Knees to the top tube on any descent over 40mph is my rule. Experienced it once and it was life threatening ... the frame was too big for me and likely had me out of position. It was a Madone and Salvodelli never had a problem decending on that bike. I would not blame the machine; a new fork maybe but not the frame.
 

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Roadbike Rider
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Headset possibly?

I have an article in front of me by Jan Heine and Mark Vande Kamp. They speculate that shimmy can be caused by bearing alignment in the headset. They cured a case of shimmy by replacing the roller bearing headset with a Stronglight needle bearing headset, supposedly better because then bearings align automatically. (No illustrations were provided and I am not sure that this headset is available in a threadless version).
 
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