NOS88

Had the strangest thing happen yesterday. Went out for my typical after work ride. Given it was raining (yet again) I thought I'd take the Camelback instead of getting all the road spray on my water bottles. Now the Camelback has about six pound of stuff in it on top of the water. (I usually take it on long trips with family members. It has a first aid kit two extra tubes, one tire, and the list goes on). In any event there is a short half mile hill about 1/4 mile long and 17% grade that I must go down to get my route started. I usually take this pretty slowly (Its narrow and very twisty for such a short run). So, I typically slide back and slightly off the saddle as I creep down. Well, yesterday I got such a strong front wheel shimmy that I almost went down. Could the extra weight on my back cause such a thing? I stopped at the bottom and checked everything. Everything seems OK. Front wheel is true with not play, fork and headset are tight. I don't know what else to look for. Got it home and took the carbon Reynolds Ouzo fork out and inspected it; it looked OK too. Any ideas of what might have been going on?

Retro Grouch 

Next time that happens, try gripping the top tube with your knees.

Allegheny Jet

How is the tire pressure? A low front tire can produce more drag causing the bike to push against the tire and not roll.

Hermes

Yes. According to Craig Calfee, bike manufacturer / owner, it usually is the fork being slightly out of alignment. A shift is the center of gravity of the system i.e. water on your back versus the bike triangle may be enough.

Were you in the drops or on the hoods? It is better to descend in the drops since it puts more weight on the front wheel and lowers the center of gravity.

I suggest taking the bike to the LBS about the speed wobble.

Hermes

You did not say how fast you were going at the time. You did say the hill is steep with curves and you take it easy. Generally, speed wobble is a higher speed problem. If you were going slow at the time, I would suspect the head set came loose. However, take it to the LBS for sure.

bobbycorno

In a word, yes. Emphatically. Weight distribuition is quite often the culprit in shimmy episodes. Case in point: I had a commuter bike that would shimmy madly if I even THOUGHT about riding no-hands, but only with the panniers on the rear rack. Move the panniers to a front lowrider rack, and it was rock solid. No hands? No prob. All day long if you want to. And no, it wasn't rack flex - both racks are Bruce Gordon CrMo jobs, probably stiffer than the frame. Just shows to go ya that bikes are awfully complex, despite their simplicity.

SP
Bend, OR

NOS88

I suspect this must have been it. I was going very slowly, not more than 6-8 mph. After I took the fork out to inspect it an reassembled everythings. The shimmy was gone.

Mojo Slim

I don't know nothin' about a low-speed shimmy, but what Retro Grouch said about clamping one's knees to the top tube is a life saver. There is much documentation about mysterious High-speed shimmies. Shimmies where the problems is never found and it never happens again. It happened to me, at about 43 mph. I almost went down, but the top tube thing saved me. I've never had the problem again.

stapfam

At this speed I am stumped. QR Not tight- Very low pressure in the front tyre- And can't think of anything else. Wearing the Camelback would only have affected a bike that is critically set up for weight distribution- at high speed and something starting it off- like a bad road surface.

Low speed like this was and I would be more inclined to look for Frame and fork problems but take it you have checked this.

cyclinfool

I had a bad shimmy once and moved my seat forward a bit - it then went away.

Cone Wrench

All together now...

https://www.youtube.com/watch?v=bqL3U...eature=related

George

kr32

Saw that one coming!

BengeBoy 

In the 80's my Univega Specialissima (which I dearly loved) would shimmy like crazy at high speeds when carrying a full touring load *if* I took my hands off the bars. If I had even the *slightest* amount of pressure on the handlebars it would stop - even just the tiniest part of the tips of my fingers on the handlebars was enough to stop it.

Of course it was impossible to resist going down mountains pressing my fingers to the bars, then letting up, then pressing down, then letting up. I was so fascinated by the violence of the shimmy that I couldn't resist inducing it for short periods of time, just to see if it was still there (it always was under full load at speeds over 30 mph or so).

I'm not sure how I lived to be 50+, but, kids - don't try that at home.

The Weak Link

Interesting thread. I've had some problem with shimmy this year and have never had the problem before. My front wheel was 1 mm or less out of true and I had it trued and my bike looked over. I experienced no twitchiness yesterday for the first time this season. I also wondered if my ahem weight redistribution (to my gluteal area) might have been responsible for some of the problem.

rumrunn6

look up the dreaded "death wobble"