Cycling in Sydney Australia
Death wobbles
I recently purchased a new, but out of production Trek Pilot 5.2 carbon fibre road bike. On my first ride it gave me a hell of a fright while riding down the hill from my home. It got the death wobbles at about 50kph. I usually ride down there in excess of 60kph without any problem.
In the 18 years since I returned to cycling I have not experienced this on any of my 3 former MTB's, my steel Trek 520 touring bike (road bike with 104cm wheelbase), nor either of my 2 tandems. In fact, I have ridden downhill at speeds in excess of 65kph on my tourer and tandems with fully laden panniers front and rear without any hint of this happening. My only recollection of a similar experience has been when I've experienced a flat on the front.
As my 4 or so rides each week each exceed 60kms, invariably I reach speeds in excess of 50kph in places, so this is a problem for me, as well as a disappointment at having shelled out some hard earned only to have the bike do this. Can anyone offer any suggestions on what may be causing it, and/or how to fix it! I'll be taking it back to the shop where I bought it tomorrow, but it would be useful to have some other input.
In the 18 years since I returned to cycling I have not experienced this on any of my 3 former MTB's, my steel Trek 520 touring bike (road bike with 104cm wheelbase), nor either of my 2 tandems. In fact, I have ridden downhill at speeds in excess of 65kph on my tourer and tandems with fully laden panniers front and rear without any hint of this happening. My only recollection of a similar experience has been when I've experienced a flat on the front.
As my 4 or so rides each week each exceed 60kms, invariably I reach speeds in excess of 50kph in places, so this is a problem for me, as well as a disappointment at having shelled out some hard earned only to have the bike do this. Can anyone offer any suggestions on what may be causing it, and/or how to fix it! I'll be taking it back to the shop where I bought it tomorrow, but it would be useful to have some other input.
Replies to This Discussion
-
Permalink Reply by Kim on -
Noelbike had the same problem with his road bike. I think it had something to do with the forks being slightly bent. All I remember was that he had to get the forks replaced and all was fine after that.
-
Permalink Reply by Neil & Alexander on -
Is that Johan Bruneeling?
(Sorry, that's a bad TdF joke.)
-
Permalink Reply by noelbike on -
Some of the carbon road bikes are pretty light. They try to be stiff around the BB but may be not stiff enough around the head. It is more of an issue on the larger sizes. There is not a lot you can do (to stop it) but something that you will want to know is how to deal with it when it happens. One trick is to clamp the top tube with your knees so as to stop the vibration that is going back through the frame. Get off the seat. Don't turn the bars.
I have been thrown off my road bike too many times and almost always ride my tourer. 80-90kph is ok on the tourer but I would not dare ride at those speeds on my road bike.
-
Permalink Reply by Darrell Stone on -
Thanks for all of your suggestions.
I took it to the bike shop yesterday and they replaced a new Bontrager tyre that wasn't quite round and tightened up the headset a little. Took it out for a run today and got the wobbles again down my home hill at the same place, so then I went further afield and powered down a hill and hit over 55 on the smooth surface of the Pacific Highway south of Swansea - not a problem. So, from all of that, the things that the lbs did probably fixed the problems, and it looks like I need to be careful of any uneven surfaces at speeds over 45-50.
-
Permalink Reply by Adrian on -
Was it a Bontrager Race-Lite tyre?
I've had a defective one of those tyres that developed an air bubble between the layers of the tyre.
-
Permalink Reply by Darrell Stone on
-
Adrian, yes it was. It also had a tear in the wall of the tyre that was a manufacturing flaw. I plan to replace them with Conti Ultra Gatorskins. They last well, roll well and I've found them to be quite puncture resistant.
-
Permalink Reply by simon t on -
Darrell - this is EXACTLY what happened to me - i had a rock solid Bianchi alu frame which i could do 75kms on easy; then sold that (big mistake) for a Wilier Izoard - a full carbon job. A week after purchase i nearly killed myself doing about 50kms down a 8%er. Went back to the store and they found that the metal insert that sits between the forks and the headset had come loose. they therefore negotiated with Wilier for a replacement set of forks and i was back on the road. HOWEVER i still get some wobbles at 60+
somehow a carbon frame just doesn't feel as tight and solid going high speed as alu. there are things one can do to offset this. after a lot of reading up on the matter i found that two things help: 'unseating' that is raising one's rear end off the seat. this transforms the 'gyro-effect' which apparently causes the wobbles. the other is to touch the knee against the top frame which again offsets gyro effects. finally i was advised not to grip the bars too tight. all in all this is better, but going full pelt down an alpine pass it isn't. of course one could go back to alu, but then one loses some of the other lovely things about carbon ...
hope this helps
simon t
-
Permalink Reply by Darrell Stone on
-
Thanks Simon. Doesn't it piss you off having ridden older bikes without these problems, and then thinking that an update of a bike will give you something better, only to find that it has problems previously not experienced and with potentially fatal flaws!
-
Permalink Reply by Tony A on -
How do the pros go downhill at 100+ km/h with their light carbon frames?
(maybe using Simon T's suggestions...)
Here are a couple of pages on "shimmy" (death wobbles) that might be useful.
http://www.sheldonbrown.com/brandt/shimmy.html
http://en.wikipedia.org/wiki/Speed_wobble
-
Permalink Reply by simon t on
-
it certainly pisses me off that i paid a lot for something that is not PERFECT in every way; but even so riding carbon is more generally a better experience than alu (IMHO) - it's a much suppler and more comfortable ride over longer distances. it just feels a lot nicer to ride, but if one has doubts at the back of one's mind descending then that's a big minus i agree.
on tony's point, if the gyroscopic thesis is correct (which seems reasonable to me) then the combination of components will change the behaviour of the bike considerably. i have a suspicion for example that the interaction of the frame and wheelset is pretty important in all this. i borrowed my neighbour's Eastons to put on the wilier and it seemed a very different bike altogether, and especially downhill (and uphill ;-) - pity i don't have the $600 at th mo to make the change ... -so it may be that pros with their access to better componentry and extensive testing are able to get around such problems ...?
-
Permalink Reply by Darrell Stone on
-
Interesting comment about the wheels, Simon. Before I bought the Trek, I read a report from another owner about how he made a big difference to his Pilot 5.2 by getting rid of the Bontrager rims. Pretty crook if you shell out the dosh and then have to get better wheels to make it work properly!
Sydney Cyclist Badge
Spread the word. Get your own Sydney Cyclist badge for your website or MySpace page. (Get Code)
© 2008 Created by DamianM
