High Speed Wobble! What to do?

I just purchased a new Specialized Tarmac three weeks ago. When I'm descending at high speeds, the entire bike wobbles very very bad. Twice this has happened to me.....I thought for sure I was a dead man! I took it back to the bike shop the first time it happened and they tightened the head set. So now today it happens again. I must add the on the down hill I'm going about 45-50 mph with some cross winds. Can anyone shed some light on this problem????

thanks

 

Bummer with a high pucker factor. With the bike newness, and assuming wheels are true and "tight", perhaps it was built with mismatched bearing parts . Kind of makes you look at getting some m/c racing leathers . Get the LBS mechanic to take her down a fast hill - at least HE will be the one to wad the bike . Good luck.

 

I will be taking the bike back to Mikes Bikes today and hopefully they will find what the problem is. After paying good money for the bike, I expected to be able to ride safe.

 

Apparently people say that speed wobbles can appear randomly to a batch of good bikes. It may have something to do with the manufacturing of your specific bike.

 

Clamping the top tube between my knees worked for me.

Also, heard that getting your bottom off the seat can stop the wobbles as well. Not game to check that one out!

 

My understanding, which I'm happy to be corrected on, is that in a case like this the bike and rider can be seen as a single unit and changing the rider may correct the problem. I find that where the hands are on the bars makes a difference; so does how I sit on the bike.
Halcyon1

 

I've the same problem with my Rabe bike.

Someone suggested different tyre pressures. I've yet to try it because I'm snowed under with work at the moment.

 

I also move my knees inward towards the top tube. Seems to work for me as well.

 

You guy's are talking about PIO - pilot induced oscillation ...
But are maybe onto something with position / CG . When on a motorcycle I will always shift weight back when the front gets "jinky" . Maybe altering bar setback & seat position ( without screwing up other parameters ) would help . This is strictly speculation on my part .

 

Here is the latest. I went back to the dealer and explained my problem a second time. The guys at Mikes Bikes were great. They told me that they wold not sell me a bike i'm not comfortable with. I test road the other Tarmac frames and the front end felt wobbly at high speed descending. At any rate, I'm again shopping for another bike. Looking for carbon with great climbing gears? Any suggestions folks? Regards,