View Full Version : Observation on speed wobble

CNY rider
09-21-2005, 07:42 AM
As this is a somewhat mysterious topic I thought I would share an experience I had yesterday.

I ride my commuter to work 4 days a week. I hit 40 MPH daily going down my hill. I've always felt stable, never a shudder. My road is rural and I'm rarely passed as I ride down.

Yesterday I had to go pick up my car at the local garage after work. It happens to be at the bottom of a different, large hill. Since I had to drive it home after, I had sandals and a few other things in my messenger bag that aren't normally there, and which increased the bulk and weight.

I rode downhill and was passed by a near continuous stream of cars. At 36 MPH there was a pronounced wobble. Enough that my heart fluttered for a second til I realized what was happening and I thought about how to deal with it. I was able to gently brake and get it back together, and the rest of the ride was uneventful.

I suspect several factors came into play: First off I was sitting more upright as I descended. If I lean too far forward the messenger bag feels like it will flip off over my head. Second, I think the increased weight on my back made my arms more rigid. And finally I think the key factor was the turbulence generated by cars going 50 MPH a foot or two away from me.

So, given that this is an otherwise stable bike, I'd say those are some factors to think about if you're having problems with speed wobble.

09-21-2005, 08:12 AM
I understand wobble is commonly caused as a result of an imbalance of weight fore and aft on the bike. Add to that a rider stiff-arming the handlebar because of the added weight of a messenger bag, and the stirring wind caused by passing cars, it would be virtually a miracle if you didn't get the wobbies.

In the future you might consider a better way to store your carried supplies (better sling perhaps), try to relax a bit letting the bike fine its own rhythm, maybe not go so fast considering all what's going on, and when the bike wants to Samba, simply squeeze your knees against the frame's top tube, squashing the tempo.

CNY rider
09-21-2005, 11:34 AM
Actually the knee squeeze on the top bar in addition to gentle braking is what stopped it.

I don't plan on bombing around in traffic at that speed with a bunch of weight on my back again!

09-21-2005, 07:21 PM
I had a similar experience last Sunday on a tour I'd never done before. I was desending after the first big climb, on a curvy road I'd never ridden, going faster than I'm used to when all of a sudden, speed wobble! I was too nervous to do much other than ride it out and feather the brakes to keep from accelerating any more. Once I got to the bottom I realized that I'd had a death grip on the bars so, on the next desent, I made sure to keep a softer grip and it was much smoother. Another desent was on a couple miles of clear, straight road, so I was comfortable letting her rip, got as aero as I can and made sure I didn't grip too tight, and no wobble, even at 40mph. I'll have to remember that one.

09-21-2005, 08:37 PM
Bro messengers ride fixies for a reasons and you found one out dude you can't load 40 pounds on your back and go down hillin at 40 m.p.h.with out risk i.m.h.o.cheers :beer: