Bike Wobble

manny-london

Hi there,

I have a Cinelli - The Machine frame which I love and have had for a couple of years. This year and on two occasions the front has started to wobble significantly when I have been on a downhill and secondly when I had just hit a pot hole. On both occasions I have had to do an emergency stop before I lost complete control. I'm trying to figure out what the problem is but haven't noticed anything obvious like a loose headset etc. Has anyone else had this problem? I am going to get the bike checked out by a mechanic but thought I would investigate some more as even he was unsure why this would be happening.

IanREmery

I've had that at speed with my new Cube Agree. Lots of theories as to what causes it, seems to be a bit of a "perfect storm" scenario where you need a few things happening at the same time. I had it when descending at about 38mph, talk about a brown trousers moment!

Couple of things to possibly check:
1. Loose stuff on the bike (as you've already mentioned)
2. Posture - Too much weight over the front seems to increase it, so get your backside over the back of the saddle more.
3. Posture - if you're not pedalling keep your feet at 3 and 6pm and keep a knee or two in contact with the top tube, this apparently helps dampen the wobble.
4. Gently apply the rear brake when it happens (for heaven's sake don't touch the front one), a change of speed can dampen the effect.
5. Loosen your grip on the handlebars when descending.

I haven't had it again since, but then I'm not sure if I've been near 38mph again since!

slowbike

The obvious one is to check the wheel & tyre are true ... anomalies will soon show when going faster.

fossyant

It's called speed wobble, and it's also common on motorbikes.

What's happened is by hitting the pot hole, you've induced the wheel and steering to shimmy, and in turn this continues. As said above, lose some speed, clamp the top tube between your legs and loosen the grip.

I used to get it on an old road bike when guards were fitted, never happened in summer ! I've also had it at about 55 mph when a side wind hit, that was a case of ease off, steady, then go for it again. No shimmy that time.

Headhuunter

fossyant wrote:

It's called speed wobble, and it's also common on motorbikes.

What's happened is by hitting the pot hole, you've induced the wheel and steering to shimmy, and in turn this continues. As said above, lose some speed, clamp the top tube between your legs and loosen the grip.

I used to get it on an old road bike when guards were fitted, never happened in summer ! I've also had it at about 55 mph when a side wind hit, that was a case of ease off, steady, then go for it again. No shimmy that time.

Yes, I've heard of this shimmy thing a few times, there are some scary clips on YouTube as well! It seems to happen mainly on downhills or fast straight sections? From what I've heard, on downhills it's best to rest 1 knee on the top tube, or push the knee slightly into the top tube, lift yourself slightly off the saddle and loosen the grip on the bars and go with the flow... I think on downhills, too many people grip the bars harder and remain firmly seated, you almost need to let the bike "flow" with the hill