|Handle Bar Wobble !!!||Fila Hebe|
Apr 13, 2002 11:29 AM
|Today during my ride I noticed that my handle bar would go into a severe wobble when descending at a high rate of speed while keeping my hands of the bars. Is this a matter of my front wheel being out of true or is there a possibility that it's something more significant than that? When I came back from my ride I stopped at my local bike shop and the mechanic did a quick little adjustment on the front wheel but the problem didn't go away. If anything it got worse in the sense that it happens at even slower speed. Any opinions will be apriciated.|
|Not your handlebars, it's your frame!||Kerry|
Apr 13, 2002 3:13 PM
|The vibration of bicycle frames is a highly complicated event. In physical terms, your bike has a resonant frequency that is stimulated when you reach a certain speed. This is not uncommon. Without any hard data, I would guess that something between 10 and 25% of road bikes have this problem. Many riders never know they have it because it occurs at very high speeds or because they don't go no-handed at these speeds. There are lots of arguments about frame stiffness, the relationship between frame dimensions, forks, headset adjustment, wheel weight, bearing adjustment, etc. Some frames will never do this regardless of rider weight, wheel weight, adjustment, etc. Some will do it regardless of these factors, and some will do it only when a certain (unpredictable) combination of factors are in play.
Headset adjustment is often pointed to as a solution, because changing HS adjustment changes the "stiffness" between the frame and fork/wheel. A headset with fretted (dented) races should be changed, so if you have "index steering" you should eliminate it - this will allow the fork/wheel to move smoothly and therefore change the effective center of mass of the system. The weight doesn't move but if the wheel and fork have a different relation in space to the frame, this will shift the resonant frequency. Often changing tires or wheels also eliminates or triggers it. Within the range of things you can change easily, look hard at the headset and clamp your knees to the top tube when descending (changes the center of mass of the frame/fork). Some say they can defeat the oscillation by letting go of the bars, or holding them very lightly. Same logic about center of mass. You may have to accept that your bike vibrates, and just deal with it.
|Not your handlebars, it's your frame!||Fila Hebe|
Apr 13, 2002 3:40 PM
|Thank you for all the information. I was hoping that it was something a little simpler then what you're suggesting but I guess I'll probably learn to live with it. I have what I like to think is a quality frame (Steelman SR) and the fork is a steel unit made by the same company. The HS is Record (threaded). My wheels are Mavic CXP 33 with 28 spikes in the front and 32 in the back. I can't quite tell from your post if the quality of the components has anything to do with this effect or is it just a flawed design somewhere in the frame.|
|I have the same problem!||skibert|
Apr 13, 2002 6:53 PM
|My bike (bianchi giro) does the exact same thing, but it does it even at slow speeds as low as 15 mph and even when I pedal. I thought it was just that my areo bars were not mounted evenly so it through my handel bar out of balence. Could this also cause it, or is the only reason the frame?|
|re: Front wheel wobble...||guido|
Apr 13, 2002 8:09 PM
|It can be caused by quick release skewer not being tight enough front or rear, either wheel being out of true or not round, spokes that are generally too loose (a "soft" wheel), rear wheel not centered (out of "dish") or not tracking front wheel, as well as headset that is too tight or "brinelled" or not floating.
Clamping knees against top tube minimizes the problem, but doesn't really solve it.
Try this: next time you go down a hill, scoot back on the saddle and lower your upper body as low as you dare, keeping your head behind the handlebars. Is the bike wobbling with your weight over the back wheel and a feather touch on the handlebars? If yes, its the bike. If no, its you: pull your upper body forward and sit up, and see if it wobbles.
If the front wheel has more bodyweight on it proportionally than the back wheel, which mountain bikers will tell you can happen automatically on a descent unless you scoot back on the saddle, any bike will wobble. If the wobble won't go away by moving around on the frame, then methodically eliminate the other possible causes, one by one, before giving up and blaming it on "resonance."
It's never a good idea to take hands off the handlebars on a fast descent. Even on a perfectly aligned bike, the front wheel has to be weighted a little with hands and forearms, to absorb shocks and hold the rubber on the pavement.
Apr 13, 2002 8:28 PM
|Interesting phenomenon: More bar pressure makes wobbles worse, as you are actually feeding more input into a front end which is trying to damp out the input of a wobbling front wheel, creating more of a wobble.
Best bet, as mentioned, seems to be to clamp the upper tube and try to have a soft touch on the bars.
|It's probably not your frame||DY|
Apr 14, 2002 9:18 AM
|If as stated above a certain small percentage of bikes (10%-25%) have this problem then according to those odds, it's probably not your frame.
You don't say in your message how long you've had your bike? Did it perform well before and then suddenly develop this problem? Did you recently change something?
I had this problem too and was very concerned it was my frame or fork. I ride some fast group training rides in close packs. On down hills we hit about 40mph. My bike was starting to "speed wobble" at about 30mph. This doesn't make for very safe conditions in a group, so I wanted to very much get to the root of this problem.
What I did was systematically eliminate items from the list of possible culprits (frame, headset, front wheel, etc). I traded front wheels with a friend and the problem was gone. Now I knew it was somewhere in my front wheel. Ended up being a bad tire, not the frame or the fork or bad headset adjustment or bad wheel.
You need to look at everything, because something as simple as a tire can really screw things up.
|It's probably not your frame||Fila Hebe|
Apr 14, 2002 10:23 AM
|Thank you again DY,
I did recently change my intire drive train from Daytona to Record. I can't tell you if it had this problem or not before because I don't recall letting go of my handle bars before at those speeds. This is my third seson with the frame. I'll start with the HS and front wheel and after that I'll just have to see. There is a very good chance that it is the tire because when looking at the tire It apears as if the rim isn't true even though it is. Thanks again and good riding.
|Is the fork original?||Alexx|
Apr 15, 2002 3:17 AM
|Sure sounds like a bike with insufficient TRAIL in the steering geometry. This usually happens when somebody replaces their stock fork with one that has too much RAKE.|| |