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Old 04-22-09, 06:23 PM   #1
MyWar
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Front wheel wobble on downhill

I was going down a long descent yesterday on my LHT. I was riding with no hands for maybe a half a mile or so, and my front wheel and bars stated to wobble rapidly. when I grabbed the bars it stopped. I let go again to see if it would do it again and it did. I kept my hands hovering over the bars at about an inch to see if it would get any worse and it didn't, really. Maybe if I had let it go longer, but I was getting a bit worried about crashing.

Is this normal? I didn't really feel like it should have been doing that. Maybe I'm wrong. I tried searching the forums for this, and I didn't find too much that was quite similar to this experience.
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Old 04-22-09, 06:51 PM   #2
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Any weight on the front end? Rack? Loaded basket?
Could be the headset. Or possible your stem/bars aren't perfectly straight/centered.
If that happened to one of my bikes, I would give it a thorough going over, or take it in to a LBS for a checkup.
Don't let it slide on the assumption that it was a fluke or won't happen again. It probably will.
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Old 04-22-09, 07:03 PM   #3
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Yeah, I had panniers on the back, but nothing up front. If there is one aspect of bicycle mechanics that I'm unfamiliar with, it's the headset/whole headtube area. So I would have to take it to a shop. Unless someone has some simple advice on checking weather or not it's too tight/loose or whatever. I just got the trucker in august from RiverCity in Portland. I guess because the bike is rather new I was assuming that the headset was not the issue. Maybe I should not make that assumption. Thanks.

Last edited by MyWar; 04-22-09 at 07:07 PM.
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Old 04-22-09, 07:06 PM   #4
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Hold the front brake TIGHT, and push forward and backward on the bike. Rock it, I guess.
Watch the headset. If you see ANY play in the cups, moving around at all, it is too loose. Hold the front end off the ground and move the bars back and forth (as if you were turning). If there is any resistance, the headset is too tight.
If you just bought the bike from a shop, I would take it in to them. They should check it out and make any repairs and/or adjustments at no charge.

Last edited by crawdaddio; 04-22-09 at 07:10 PM.
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Old 04-22-09, 08:32 PM   #5
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that's the wild phenomena known as the death wobble - look it up - wild you tube videos too. you gotta lower your center of gravity by standing on the pedals or grip the horizontal bar with your knees, or both.

I got it once cranking as fast as I could down a hill - almost killed myself
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Old 04-22-09, 08:36 PM   #6
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It happens on my bike around 40mph, which is a bad speed for it to happen because it scares the crap out of me. I think it is due to a natural vibration in the bike. Try gripping the top tube with your knees, that will dampen the vibration, and it cuts short the wobble for me.

The first time it happened to me I almost hit a curb at high speed, it is scary
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Old 04-22-09, 09:04 PM   #7
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Originally Posted by rumrunn6 View Post
that's the wild phenomena known as the death wobble - look it up - wild you tube videos too. you gotta lower your center of gravity by standing on the pedals or grip the horizontal bar with your knees, or both.

I got it once cranking as fast as I could down a hill - almost killed myself
This happens to touring bikes when people have the back end to loaded and not much up front. You can find this phenomena all over the touring threads. To fix it you have to distribute your goods, side to side and front to back.
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Old 04-22-09, 09:51 PM   #8
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Awesome! That makes a lot of sense because I had only one pannier in the back and nothing in the front. I did also check the headset and it didn't seem loose or tight. So I guess it was probably an issue of weight distribution. I must have been going pretty fast, no computer on the bike, but I would guess at least 30mph. It was a really long decent, probably eight miles or so. Thanks!
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Old 04-22-09, 11:11 PM   #9
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They put dampeners on motorcycles to avoid the death wobble, at high speeds. Imagine doing 80mph and having the bars start jumping around. I'm pretty sure I'd crap my pants first and then put the motorbike up for sale.
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Old 04-22-09, 11:27 PM   #10
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This happens to touring bikes when people have the back end to loaded and not much up front. You can find this phenomena all over the touring threads. To fix it you have to distribute your goods, side to side and front to back.
this. It gets worse when you sit up because your body weight moves back onto the rear wheel. Scary, isn't it?
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Old 04-22-09, 11:36 PM   #11
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A couple of things can cause the wobble.

First is the "critical speed" rpm of the wheel itself. Bicycle wheels are not balanced very pefectly, so they tend to hit critical speed rpm at fairly low speeds like under 60 mph.

Second, and probably most responsible for the shaking is that the forks aren't perfectly true. Many forks aren't perfect to begin with. Add to that some front end bumbs, pot-hole whammies, and other road hazards, and the forks can come out of alignment.

Headset bearing tensioning is critical. Is your headset a sealed headset unit like a cartridge, or is it old school? If it is old school, then it can be overtightened or loose - neither are good. You will most notice overtightened bearings because it is more difficult to ride no-hands. Crawdaddio (above) talks about the breaking/rocking test for checking if the headset is loose.

I was bicycling down a mountain in China once and the friction from the brake pades against the rims heated up the wheels so that they warped. As I gained speed, the problem got worse until it looked like my tires were made our of spagetti. Of course, the bike was shaking like an alchoholic at double-bubble.
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Old 04-22-09, 11:36 PM   #12
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Yeah, at first I was just sitting back chillin' enjoying the downhill. I was leaning back too. So yeah, it scared scared me quite a bit.
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Old 04-23-09, 09:00 AM   #13
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Good suggestions from everyone regarding headset, weight distribution on the bike, etc.

I've got a Cross Check, and I get speed wobbles between 17.5 and 19.5mph depending on how much weight I have in my front bag. Headset isn't loose, wheels are true and round, all the usual things check out just fine. I'm convinced that every bike has a no-hands wobble speed; I just haven't found it on all of mine yet.

My Paramount gets 'em at 23mph
My Cross Check is 17.5 to 19.5
Not sure on my Trek 400 or MTB utility cruiser.
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Old 04-24-09, 11:18 AM   #14
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It may have been caused from the lack of weight on your front tire, in conjunction with any irregularities/bumps in the road. If your rear rack was loaded, that would pull even more weight from the front, increasing the chances of the wobble. you could try to weight the front a little, and then repeat the incident to see if it happens again. Sounds like your headset may be loose as well.

I had this happen on a motorcycle at @ 115 mph indicated. It was a good thing that there was no traffic on the highway and that I had all six lanes to myself, because i was in that sixth lane before the bike came back under control.
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Old 04-24-09, 11:52 AM   #15
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Ran into the wobble zone recently on my Point Reyes at about 35mph when I ran it with a large rearward weight bias. It never got scary, but hadn't encountered it in a long time. Had a beefy rear rack with a frame bag on top, so it was a bit top heavy too. Ditched that combination and the problem went away. I'm an unusually light rider, but don't know if that would add to the wobble or tend to delay it.

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