Bicycle Mechanics - Help: Random head set wobble at speed; 2010 Look 566

Bike was wobbling out the gate downhill at 40 mph.

MEchanic took it apart, rebuilt with torque wrench at 1 month tune-up;

Recently, (9 months later) wobble back; downhill at about 28-30 mph, and still wobling as I slowed to 21 mph;

on same bike ride, did not wobble on the way back at 25-30 mph?

suggestions, please. FSA headset.

SEE PHOTO in first thread reply

https://mail.google.com/mail/?ui=2&ik=c5cb61c7bd&view=att&th=12f8de0bbf444d57&attid=0.1&disp=inline&zw

When stationary, if the brakes are applied, is there any movement in the headset if the bike is rocked? if so, get it fixed, problem solved.

Bike was wobbling out the gate downhill at 40 mph.

MEchanic took it apart, rebuilt with torque wrench at 1 month tune-up;

Recently, (9 months later) wobble back; downhill at about 28-30 mph, and still wobling as I slowed to 21 mph;

on same bike ride, did not wobble on the way back at 25-30 mph?

suggestions, please. FSA headset.

SEE PHOTO in first thread reply

What you have is a death, or speed, wobble
(http://en.wikipedia.org/wiki/Speed_wobble). This from the article


The top five influences on wobble have been found to be lateral stiffness of the front tire, steering damper, height of bike center of mass, distance of bike center of mass from rear wheel, and cornering stiffness of the front tire.

is a good explanation of what you are experiencing. It's rather amazing that this doesn't happen all the time on bicycles. When you have a vehicle with a light frame (low lateral stiffness), no steering damping, high center of gravity and short wheel base, it's a wonder that bikes don't wobble all the time. The only thing going for it is the stiffness of the tire.

Tighten your headset properly to correct the problem. When it happens you can dampen the oscillations by touching the top tube with your knee. Proper tire inflation, or changing the tire inflation, may help too.

1. Tires inflated pre-ride; rear to 120 lbs, front to 115.

2. Dont have a torque wrench, even if I di, dont know to what degree to tighten, afraid to overtighten headset and crack carbon frame.

3. Lower tire inflation; will that help?

1. Tires inflated pre-ride; rear to 120 lbs, front to 115.

2. Dont have a torque wrench, even if I di, dont know to what degree to tighten, afraid to overtighten headset and crack carbon frame.

3. Lower tire inflation; will that help?

You might try a lower inflation. It's hard to tell if it would work. There are many factors that are involved with death wobbles and it's tough to juggle them all to make the problem go away. You should try all kinds of things and see what works best. The knee to the top tube is probably the best way to stop the wobble immediately so that you don't crash.

Check with the mechanic who worked on the bike to begin with or the fork manufacturer. If the fork has a carbon steer tube, you have to be careful about torque. If it has a aluminum steer tube, you don't have to be as careful. Basically, you want the headset to have no play yet rotate easily. There's not a lot of force that needs to be put on the top cap to achieve this. Probably on the order of inch pounds.

my common sense tells me not to use a torque wrench on the pre-load! Is your reflector still on the wheel?

I usauly run my front tire 90-100 and never have had a problem.