Speed Wobbles

I recently bought a second hand Bianchi Reparto Corse Lite Alloy that was manufactured in 2000. There is no damage to the frame what so ever. I have Campagnolo Record groupset throughout, with a Bianchi headstem and ITM handle bars. The forks are Bianchi Engineered Carbon.
Question - The handling of the bike is quite good and decending it picks up speed quickly. The problem is that when you get to around 75-80kph you get really nasty speed wobbles and until you get down to about 60 they dont go away. Of course doing this speed down 6%+ gradients and getting speed wobbles tends to cause about 200L of adrenaline to be pumped around the body and makes you face look like . My question is, what causes the speed wobbles and apart from not going that fast is there anything I can do to prevent it.
I have raced competitavely for around 10years and never experienced this before, people I talk to say it is usually the headset being loose - but the headset is fine. Other have said that it is the forks?? Nobody seems to be able to pin point it. Any help would be appreciated.
I would like to change back into

 

G'day,

as per your other advice, I reckon it will definately be 'front end'. If you've checked the headset & forks. I'm assuming a 'high end' bike like that will have 'high end' wheels & hubs, so you can probably dismiss them from the equation, (unless they are damaged)....perhaps check the tread pattern & the 'true' of the wheel. I had a similar problem awhile back when sprinting. Turns out I was pulling so hard on the bars that the front wheel was 'lifting'lightly with each pedal stroke, causing what I thought was a 'speed wobble'. Good luck with your problem. Make sure you post the solution when you find it,


cheers,

Hitchy

 

It could be alot of things, but not the HS if its installed correctly and tight. There are lots of mechanical possibilities,including wheels.It can also be caused by the frame,and not due to any damage or necessarily mis alignment.It just happens,under certain conditions and more oten with larger frame sizes.It can often be stopped by clamping knees to toptube.

 

It's not necessarilly 'definately the front end'.

 

Which way do you have your headstem(ahead) pointing up or down. A guy I know had speed wobbles,made the stem point down and he never had a problem again.

 

It would point up but only by a couple of degrees. To make it point down I would need to but a different headstem. Thanks for the suggestion.

 

Yeah I was wondering if it was the angles of the frame. Its only a 54cm and I have travelled down the hills its happend on so many times before and at various speeds, 75-90kph. I will give the knees together idea a go in the future.

I dont think it will be the wheels as it has happend with two different sets. I have used my wheels from my previous bike (chorus with mavic open 4 cd) and the new bikes wheel (record also with mavic rims).

Thaks for your comments

 

I ride a Bianchi San Remo (light touring) that has the same problem above 60 kmh. It's a Cro-Mo frame and fork and I was thinking of changing to a carbon fork in the hope of fixing the problem. My previous bike was a Wheeler Cro-Mo hybrid and it did the same thing. The Bianchi is a real disappointment that it does the same. The dealer was no help at all. I'm stumped.

 

Trek made a touring bike years ago that I think was the Trek 620. It was designed as a touring bike and it had wobbles when the frame had some panniers on it just riding across a parking! Trek said that they put too light of a TT on the frame and after some protesting they sent him a new frame with a heavier TT and it solved the problem. The frame and fork alignment were good. You did not say how much you weighed but if you are heavy that could contribute to the problem. I also had a great racing bike years ago and had incredible speed wobble at speed and the wheels that I had built seemed to be the culprit. I changed the wheels out to another set and the problem went away. I gave those to my old girlfriend and she never had any problems but she was short and 98 pounds. I loved those wheels and she still uses them today. I think that the problem was a balance problem with the weight. It is always a tough job finding the problem.

 

I too have had the problem above 75 kph, which is strange because the bike handles beautifully at around 70.
i have often thought it is me getting nervous and handling the bike badly. The wobble definitely is not wheels or headset, but flex in the frame. I am tall, riding a big frame which is some fancy superlite steel and has a lot of flex. (daccordi 'profidea' frame).
what happens is i might hit a bump when my weight comes back onto the peddles it seems to flex the frame. That flex will then generate at an enourmous rate to the point of a massive whip running through entire bike. It is a real challenge to stay on, but in the three instances of it happening I haven't come off, but have had to basically stop before the whip dissappears,
What I want to know is given this flex problem, is it best to hold the bars really tight when descending or lightly?
basically it is too dangerous for me to ride this bike much above 70kph, which isn't good for racing