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passive/aggressive
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Discussion Starter · #1 · (Edited)
speed shimmy rant

This weekend I finally managed to eke out a ride so I headed up Mt Lemmon to the 7 cataracts. Planned on going farther but the high temps kept me lower (ironically as it would be cooler higher). Anyway whilst descending I came to an area that is fast and straight so me being on a new bike and hitting this for the first time on a bike made in this decade I started to give it. At around 35mph killer speed wobble. Managed to reel it in and slow and upon stopping the first thing I did was check the rear QR which was not only loosely applied but not seated in the dropouts fully on one side.

Needless to say I resumed down the remaining 5-6 miles gingerly, on top of the hoods and terrified. After some research I realized that the QR was probably the culprit but I am going to replace the headset, true up the wheels, and more than likely replace the fork (litespeed house brand that is quite noodly anyway).

So the rant is how do I go out and test this again? Do I return to the location of the previous shimmy and try to replicate it? What if a cross wind was part of the shimmy? How do I ensure that I can ride this bike? What if it happens again? Do I get rid of the first road bike that i have purchase new since 1986? Buy a stiffer bike? Dang trying to not out think myself here too...

Any advice would be appreciated.
 

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Whoa, just calm down a little and take it easy. Don't go replacing things until you check one thing at a time. First make sure the wheels are true, and spoke tension is okay. Then check the headset adjustment for any looseness. Take it out on a reasonably fast descent and increase speed gradually and see what happens. Get in the drops, with weight back and low (on the hoods is a less stable position -- I don't know why you went there after your incident). If it starts to shimmy, try standing up slightly, with cranks level, butt a little behind the saddle, and grip the top tube with your knees, while your thighs grip the saddle nose.

And if you think you really need to replace things or make major adjustments, do one at a time. Shimmy is a complex phenomenon of resonance. Changing the mass or elasticity of one part of the system may solve it. But I'd start by examining headset condition and adjustment, and wheel condition. And I'd give the whole bike a good inspection. How the heck did you manage to start on a mountain ride with the rear wheel improperly installed? You need to acquire some good pre-ride inspection habits, IMHO.

Don't panic.
 

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passive/aggressive
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Discussion Starter · #3 ·
Thanks

I have run through those things. Not sure how the rear wheel got like that actually. Can't think when the last time I wrenched and didn't double check the rear wheel after I took it out of the stand but can I now guess it was recently.

The wheels are clean and well tensioned. I am going to hit them with the tensionometer again just to be certain but they are well seasoned wheels that I built and used previously on my old bike without any odd efffects. I do wonder about the response of the new bike which is substantially lighter than the old one, in the realm of 6-8 lbs, and whether a defect in the wheel build or tires (which are new) resonates in the new frame because of this.

The headset is a canecreek S3 (?) that came stock with the bike but I have adjusted it recently. The forks is a thorn in my side flexing whenever I get out of the saddle to crank up a hill or sprint or anything. Made my spoke magnet hit the receiver at all locations on the leg until I mounted it right by the hub. Very flexy IMHO.

Thanks for the information on how to test though. I felt more stable on the hoods and the air against my body keep me slow enough not to cross over into the 30's or ride the brakes all the way down. I will head out this weekend and try the pinch the bike thing and let the speed amp up a slowly and hopefully it was just the QR. Any bike upgrades will not be done before I figure it out. Just planning them, especially the fork which just rubs me the wrong way.
 

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A shimmy could be a number of things and as recommended you should make sure your bike is adjusted properly and do a rule out one @ a time.

Where I ride I hit down hills at 40 to 50 miles per hour every day. I ride a 2001 litespeed Tuscany, with both the OEM Look fork and now with an Easton EC90SLX without any problems. I would sure hate to think that I would need to keep it under 35-30 miles an hour. It would take much of the fun out of the ride.

Poorly adjusted headsets are the usual problem but other things can also contribute, wheels, tires, misaligned fork or frame, however, Litespeeed is known for their quality and tight tolerences so I doubt that is the case but you never know.
 

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Discussion Starter · #5 ·
Yes years of riding a slightly too small cyclocross frame as my road bike finally led up to a purchase of a litespeed siena and I love it. Being afraid to let it roll would really suck as I have 27miles of amazing twisty turny scenic route mountain road 20minutes from my door.

I feel like the culprit is the QR but I also feel like the fork is totally bogus as it always has a hunting feel about it like it is searching for a line whenever I ride it. Real Design fork: looks flexy and feels flexy and at 200lbs I can notice that kinda stuff I think.
 

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Some other conditions to consider are road surface. I get a shimmy on the same chip and seal road all the time at 30 mph, when I move to the smoother portions of the road it goes away. I also find that a side gust of wind will start it. I find staying relaxed with elblows bent to absorb shock helps.
 

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A lot of cases of shimmy are caused by the rider not being relaxed on the bike. It's a feedback system- you get a little wiggle and grip the bars tighter which makes your shoulders part of the system and increases wiggle, etc.

The fix for that is to keep your elbows bent and relaxed. And grip the top tube with your knees.
 

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rockcrusher said:
Yes years of riding a slightly too small cyclocross frame as my road bike finally led up to a purchase of a litespeed siena and I love it. Being afraid to let it roll would really suck as I have 27miles of amazing twisty turny scenic route mountain road 20minutes from my door.

I feel like the culprit is the QR but I also feel like the fork is totally bogus as it always has a hunting feel about it like it is searching for a line whenever I ride it. Real Design fork: looks flexy and feels flexy and at 200lbs I can notice that kinda stuff I think.
It sounds like you really want that new fork, for lots of reasons. You should probably just go ahead and get it. Even if the fork isn't "the" reason for the shimmy (i.e., it's only part of a complex interaction), there's a fair chance that changing it out will remedy the problem, by significantly altering the characteristics of a major component of the system.
 

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Discussion Starter · #10 ·
ericm979 said:
A lot of cases of shimmy are caused by the rider not being relaxed on the bike. It's a feedback system- you get a little wiggle and grip the bars tighter which makes your shoulders part of the system and increases wiggle, etc.

The fix for that is to keep your elbows bent and relaxed. And grip the top tube with your knees.

yeah I got a lot of that going on too. New bike....heck new concept of road bike for me... and first real descent, I can say with certainty that I was nervous and excited and probably too rigid too. I am an open vessel so I will try to relax and hit the same section this weekend. No changes except settled QR's and tuned bike.

The fork will happen because yes I hate the OEM one and want a new one.
 
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