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#1
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Downhill Shimmy
A few weeks ago, I experienced, for the first time, that I am getting front wheel wobbling on descents. It was on a steep hill that I have been down time after time, but this day I was scared half to death that I was going to lose control of the bike and eat the pavement. I look my bicycle over, but I can't see any mechanical problems that might cause that to happen. I seem to be tensing up on descents when I didn't used to have that problem. Since those few weeks ago, I am still experiencing the same effect and it is very scary. The people behind me immediately try to pass me for fear they may end up going down if I go down. It's become very annoying. It feels more psychological than anything else. I have lost a bit of weight lately from all the riding I have been doing, so I am flying up hills with relative ease where I used to get dropped before, but now I am losing a grip on descents when I used to fly down hills ahead of everyone else, even when I wasn't aero, because my weight giving me advantage. However, now that I am losing the weight, I seem to be shimmying like crazy. It's become like a roller coaster feeling. One rider, who is a fellow team mate, and is a cat 3 racer, told me to try pulling my knees in using my them to pull up under the top tube and sit back farther on the seat and get more aero, but I still feel like I am shimmying, and he noticed that I was to, even going down a hill at a mere 25 mph. Finally, I tried turning the biggest gear on the bike while going down hill, or at least spin the pedals even if it wasn't giving me momentum, and it seemed to help. I felt more stable, like my center of gravity was under better control. Does anyone have any advice to help me conquer this newly chronic problem? |
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#2
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Downhill Shimmy
A few weeks ago, I experienced, for the first time, that I am getting
front wheel wobbling on descents. It was on a steep hill that I have been down time after time, but this day I was scared half to death that I was going to lose control of the bike and eat the pavement. I look my bicycle over, but I can't see any mechanical problems that might cause that to happen. I seem to be tensing up on descents when I didn't used to have that problem. Since those few weeks ago, I am still experiencing the same effect and it is very scary. The people behind me immediately try to pass me for fear they may end up going down if I go down. It's become very annoying. It feels more psychological than anything else. I have lost a bit of weight lately from all the riding I have been doing, so I am flying up hills with relative ease where I used to get dropped before, but now I am losing a grip on descents when I used to fly down hills ahead of everyone else, even when I wasn't aero, because my weight giving me advantage. However, now that I am losing the weight, I seem to be shimmying like crazy. It's become like a roller coaster feeling. Have you read the FAQ on bicycle shimmy, found here- http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html? It covers the subject very well. But reading your post, it really appears that you've already figured out what's caused it- your loss of weight. You've changed how you interact with your bike. Remember that a bike isn't stable without the help of someone on it, and, well, you changed. That's not to say there might be something going on with the bike, but we do know, for a fact, that the most-significant variable, you, are different now than when the bike didn't shimmy. The question is, what can you do about it? That's a really tough one, because once you've lost confidence in a bike, you approach it in a way that makes it more likely to shimmy (by being, as you said, tense). You might need to make some sort of major change in your position, for no good reason other than to force you to do things differently than before, and make it feel as though something has really changed. I've seen cases where it just doesn't matter; once someone's lost faith that their bike will be stable, there's nothing you can do to change it. It becomes a self-fulfilling prophecy. But first, if you haven't read the FAQ, do so. It often helps to read an authoritative, unattached (to your situation) view of the problem, and potential solutions. --Mike-- Chain Reaction Bicycles www.ChainReactionBicycles.com "Michie" wrote in message oups.com... A few weeks ago, I experienced, for the first time, that I am getting front wheel wobbling on descents. It was on a steep hill that I have been down time after time, but this day I was scared half to death that I was going to lose control of the bike and eat the pavement. I look my bicycle over, but I can't see any mechanical problems that might cause that to happen. I seem to be tensing up on descents when I didn't used to have that problem. Since those few weeks ago, I am still experiencing the same effect and it is very scary. The people behind me immediately try to pass me for fear they may end up going down if I go down. It's become very annoying. It feels more psychological than anything else. I have lost a bit of weight lately from all the riding I have been doing, so I am flying up hills with relative ease where I used to get dropped before, but now I am losing a grip on descents when I used to fly down hills ahead of everyone else, even when I wasn't aero, because my weight giving me advantage. However, now that I am losing the weight, I seem to be shimmying like crazy. It's become like a roller coaster feeling. One rider, who is a fellow team mate, and is a cat 3 racer, told me to try pulling my knees in using my them to pull up under the top tube and sit back farther on the seat and get more aero, but I still feel like I am shimmying, and he noticed that I was to, even going down a hill at a mere 25 mph. Finally, I tried turning the biggest gear on the bike while going down hill, or at least spin the pedals even if it wasn't giving me momentum, and it seemed to help. I felt more stable, like my center of gravity was under better control. Does anyone have any advice to help me conquer this newly chronic problem? |
#3
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Downhill Shimmy
Michie, you say you have lost "a bit" of weight. Sounds like it may be
"quite a bit," since you are now flying up hills. I think Frank is right--you and the bicycle together are a dynamic system, and sometimes a seemingly small change can move things to an unstable combination. Why don't you try adding back the weight by filling your pockets and/or a backpack with heavy stuff, and see what effect it has? |
#4
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Downhill Shimmy
Have you tried another bike just to rule out a mechanical problem?
The only time it ever happened to me was when my headset was loose (even though the locknut was tight) so make sure it is adjusted correctly. Scared the sh*t out of me too. Make sure the front wheel is evenly mounted too. Apologies if this is all obvious to you, Z "Michie" wrote in message oups.com... A few weeks ago, I experienced, for the first time, that I am getting front wheel wobbling on descents. It was on a steep hill that I have been down time after time, but this day I was scared half to death that I was going to lose control of the bike and eat the pavement. I look my bicycle over, but I can't see any mechanical problems that might cause that to happen. I seem to be tensing up on descents when I didn't used to have that problem. Since those few weeks ago, I am still experiencing the same effect and it is very scary. The people behind me immediately try to pass me for fear they may end up going down if I go down. It's become very annoying. It feels more psychological than anything else. I have lost a bit of weight lately from all the riding I have been doing, so I am flying up hills with relative ease where I used to get dropped before, but now I am losing a grip on descents when I used to fly down hills ahead of everyone else, even when I wasn't aero, because my weight giving me advantage. However, now that I am losing the weight, I seem to be shimmying like crazy. It's become like a roller coaster feeling. One rider, who is a fellow team mate, and is a cat 3 racer, told me to try pulling my knees in using my them to pull up under the top tube and sit back farther on the seat and get more aero, but I still feel like I am shimmying, and he noticed that I was to, even going down a hill at a mere 25 mph. Finally, I tried turning the biggest gear on the bike while going down hill, or at least spin the pedals even if it wasn't giving me momentum, and it seemed to help. I felt more stable, like my center of gravity was under better control. Does anyone have any advice to help me conquer this newly chronic problem? |
#5
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Downhill Shimmy
Have you tried another bike just to rule out a mechanical problem?
Riding another bike does nothing to rule out a mechanical issue, unless the other bike were in every way identical. Even then, the psychological component of shimmy... just knowing that there *might* be something wrong with your old bike that isn't with the new one... that alone might create the confidence or lack of being tense that could have caused the issue on the first bike. It's not often as simple a problem as it appears. --Mike-- Chain Reaction Bicycles www.ChainReactionBicycles.com "Zimmy" wrote in message ... Have you tried another bike just to rule out a mechanical problem? The only time it ever happened to me was when my headset was loose (even though the locknut was tight) so make sure it is adjusted correctly. Scared the sh*t out of me too. Make sure the front wheel is evenly mounted too. Apologies if this is all obvious to you, Z "Michie" wrote in message oups.com... A few weeks ago, I experienced, for the first time, that I am getting front wheel wobbling on descents. It was on a steep hill that I have been down time after time, but this day I was scared half to death that I was going to lose control of the bike and eat the pavement. I look my bicycle over, but I can't see any mechanical problems that might cause that to happen. I seem to be tensing up on descents when I didn't used to have that problem. Since those few weeks ago, I am still experiencing the same effect and it is very scary. The people behind me immediately try to pass me for fear they may end up going down if I go down. It's become very annoying. It feels more psychological than anything else. I have lost a bit of weight lately from all the riding I have been doing, so I am flying up hills with relative ease where I used to get dropped before, but now I am losing a grip on descents when I used to fly down hills ahead of everyone else, even when I wasn't aero, because my weight giving me advantage. However, now that I am losing the weight, I seem to be shimmying like crazy. It's become like a roller coaster feeling. One rider, who is a fellow team mate, and is a cat 3 racer, told me to try pulling my knees in using my them to pull up under the top tube and sit back farther on the seat and get more aero, but I still feel like I am shimmying, and he noticed that I was to, even going down a hill at a mere 25 mph. Finally, I tried turning the biggest gear on the bike while going down hill, or at least spin the pedals even if it wasn't giving me momentum, and it seemed to help. I felt more stable, like my center of gravity was under better control. Does anyone have any advice to help me conquer this newly chronic problem? |
#6
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Downhill Shimmy
"Zimmy" wrote:
Have you tried another bike just to rule out a mechanical problem? Even if a different bike did not shimmy, it wouldn't prove there's a mechanical problem on the first bike. Shimmy is all about resonance, and the interaction of bike and rider. A different rider on the bike probably wouldn't get the shimmy. Art Harris |
#7
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Downhill Shimmy
"Art Harris" wrote in message ps.com... "Zimmy" wrote: Have you tried another bike just to rule out a mechanical problem? Even if a different bike did not shimmy, it wouldn't prove there's a mechanical problem on the first bike. Shimmy is all about resonance, and the interaction of bike and rider. A different rider on the bike probably wouldn't get the shimmy. OK, perhaps "rule out" was the wrong term, however if a few different riders all got a shimmy on the OP's bike then it could indicate a mechanical problem, right? Z |
#8
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Downhill Shimmy
Michie wrote:
A few weeks ago, I experienced, for the first time, that I am getting front wheel wobbling on descents. It was on a steep hill that I have been down time after time, but this day I was scared half to death that I was going to lose control of the bike and eat the pavement. I look my bicycle over, but I can't see any mechanical problems that might cause that to happen. I seem to be tensing up on descents when I didn't used to have that problem. Since those few weeks ago, I am still experiencing the same effect and it is very scary. The people behind me immediately try to pass me for fear they may end up going down if I go down. It's become very annoying. It feels more psychological than anything else. I have lost a bit of weight lately from all the riding I have been doing, so I am flying up hills with relative ease where I used to get dropped before, but now I am losing a grip on descents when I used to fly down hills ahead of everyone else, even when I wasn't aero, because my weight giving me advantage. However, now that I am losing the weight, I seem to be shimmying like crazy. It's become like a roller coaster feeling. One rider, who is a fellow team mate, and is a cat 3 racer, told me to try pulling my knees in using my them to pull up under the top tube and sit back farther on the seat and get more aero, but I still feel like I am shimmying, and he noticed that I was to, even going down a hill at a mere 25 mph. Finally, I tried turning the biggest gear on the bike while going down hill, or at least spin the pedals even if it wasn't giving me momentum, and it seemed to help. I felt more stable, like my center of gravity was under better control. Does anyone have any advice to help me conquer this newly chronic problem? Aside from other responses, I'd first check the bike over carefully to rule out anything mechanical or structural (as best as I could). Headset tight? No loose bolts? Fork and frame all sound? Spokes in good shape? Tires on right? Put some stress on things and listen for pops or creaks. Once you're confident that the bike is good, try a different front wheel and see if the shimmy goes away. Does it only do it on this one hill? Sounds almost like there's a "shimmy point" where at a certain speed or place you get the shake? Maybe once you know the bike's OK, you can sort of blast through it by /increasing/ your speed? IOW, I got nuthin'... Good luck! |
#9
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Downhill Shimmy
Michie wrote:
A few weeks ago, I experienced, for the first time, that I am getting front wheel wobbling on descents. It was on a steep hill that I have been down time after time, but this day I was scared half to death that I was going to lose control of the bike and eat the pavement. I look my bicycle over, but I can't see any mechanical problems that might cause that to happen. There are no "problems" specifically. The difficulty is that a bike/rider system has modes of oscillation that are almost undamped. Under the right conditions, almost any bike/rider will experience shimmy. What those conditions are varies with the specifics. Each bike/rider is different. Someone else can get on the same bike, go down the same hill, and not experience any shimmy. You may experience it every time you go down that hill. The conditions needed to produce the shimmy are almost chaotic, that is, a very small change in the way you sit, or the wind, or the tires, whatever, can change a no-shimmy descent into a scary one. But that is also the solution. Change anything, and the shimmy will probably stop. I had a bike that would shimmy on downhills. I learned to raise my butt up off the saddle, and it disappears, immediately. Try that. It's the cheapest solution. Others will tell you that you need new wheels, new tires, or a new stem. Or perhaps the headset is too tight, too loose, or the wrong brand. The point is, if you change anything, you change the system, and so you change the shimmy conditions. All the advice is right, in that whatever you change will fix the problem. Mine is the cheapest advice. Get off the saddle. Getting your butt off the saddle makes a huge difference in the system, since you deny the pivot point for the twisting back and forth that is what shimmy is. Without the pivot, the motion dies immediately. On the other hand, gripping the bars harder, which is the natural reaction, reinforces the motion. I seem to be tensing up on descents when I didn't used to have that problem. Since those few weeks ago, I am still experiencing the same effect Because you are tensing up. It's become very annoying. It feels more psychological than anything else. No, it is not psychological. But it seems that way because it is a positive feedback loop when you tense up. Does anyone have any advice to help me conquer this newly chronic problem? Lots of advice coming, I am sure. -- David L. Johnson Arguing with an engineer is like mud wrestling with a pig... You soon find out the pig likes it! |
#10
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Downhill Shimmy
Zimmy wrote:
OK, perhaps "rule out" was the wrong term, however if a few different riders all got a shimmy on the OP's bike then it could indicate a mechanical problem, right? There is no "mechanical problem", even though changing damn near any part of the bike will fix the problem. -- David L. Johnson Arguing with an engineer is like mud wrestling with a pig... You soon find out the pig likes it! |
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