I just got back form a bike ride in which I had a near death experience. Coming down a slightly bumpy road, with a cross wind from the right, at about 29 mph, my bike began to shake side to side violently. I was not in the aero position when it occurred and only by the grace of GOD did I not die today. I inspected my bike and everything appears to be fine. I really need to find out what caused this to prevent it in the future. Can anyone offer advice or insight.
Were you going down hill? The “death wobble” has been discussed here several times. Do a goggle and you should find lots of info.
My TCR will do that sometimes on fast down hills. Very, very scarey. The cure is to grip the top tube between your knees and unweight your butt off the saddle a bit. Stops the wobbles fairly quickly.
what cerveloguy said. It is worth pointing out: This is almost certainly not the bike causing this, or at least not the bike exclusively.
Doesn’t only happen with bicycles:
This same thing happened to me on my Trek 5200 this summer in the same conditions. When it happened to me I was holding on for dear life and it did not stop until the bike came to a stop. I come from the motorcycle road racing and there this would be called a tank slapper. After talking with club members and then looking on the net and found this has happens to many people. The crosswind and road conditions cause a vibration in the frame that then causes the bike to go into a wobble. The stories I read read about say the best way to stop it is for press you knee into the frame to stop the vibration and also to hold the bars more to the center. Fighting it on the brakes down on the drops makes it worse. I have the knowledge now so hopefully it will not happen again and I will be more aware of those conditions in the future.
Rod
I think this has to do with something called resonant frequeny. For simple objects, its easy to find it’s resonant frequency, but for complex objects, such as a person on a bike, its much more difficult (speed, weight, road surface vibration, wind, tire surface, etc). Even bridges and buildings have a resonant frequency.
I second (or third?) the advice provided. I had this experience coming down Yellow Lake (before they repaved and got rid of the tar snakes). Very freakin’ scary. Best advice is to clamp your knees against the top tube. Go easy on the steerer (don’t fight it) and do not slam on the brakes.
This is an issue of resonant frequency (where the cycles basically amplify themselves - there is one example of the Tacoma Narrows Bridge, where resonant frequency actually destroyed the bridge!). By dampening the resonance with your knees, you’ll settle them down. You cannot counter the vibrations quickly enough to dampen them with the handlebars/steerer - you’ll probably only succeed in amplifying them.
I’ve heard that some bike designs are better at handling this (or avoiding it altogether), but I think it can happen to any bike and any rider - the reaction to it is key to managing it (i.e. I’m sure the best bike handlers feel this coming on before it becomes an issue…).
ccy
I agree with all the advice given above on how to stop it after it starts. But there could be a cause that is simple to fix. I had it happen on my QR Caliente at 42mph training on the World’s Toughest half course on the down hill leading to the narrow bridge that is also the tallest bridge in California. A truck passed me at 60 and I went into the most frightening few seconds of my life. The knees on the top tube did the trick but I still needed a clean pair of bike shorts. I found that the adjuster screws in the rear facing dropouts were not even. This caused the rear tire to point slightly to the left. I believe that to be the cause and after correcting I have had no more problems. Check your clearance on the P3 cutout to see if the tire is even.
Dave
Some offset / rake on carbon forks is too short , add in a long stem and rider weight too far back , a bit of headset play,bingo your wooblin. I could get my lotus to do it by sitting up and tap to bar end.
I also find that threadless headset never keeps bearing pressure as well as,an old thread headset .
It could likely be the ‘death-wobble’, but it could also be the bike. Not actually the bike itself, but the set-up of the bike. I have a P3 that I’m selling because, although it is the correct frame size for my body dimensions, this bike cannot be made to fit me. I saw one of the best fit specialists on the east coast who is well regarded in this forum and everywhere else. I spent nearly an entire day with him… and the result… an unstable bike at best. For my short-torso, the top tube is too long and the head-tube is too low. Set up in a steep position with the short head tube, I need a bunch of spacers and a rising stem. Ves Mandaric told me this is the equivalent of having Formula F1 handling/touchiness of steering, in a double-decker bus. I 100% completely agree and have the scars to back up that theory. With its current set up by one of the most well regarded fitters in the world, this P3 is jittery on any road that is not perfectly smooth.
I now have a completely custom bike that was built to my dimensions with an aggressive position that I can ride comfortably and confidently through anything. In fact, in a hairy situation during the state TT, I even took it off-road for several hundred yards avoiding a car in the pouring rain…and still won my CAT.
Sorry to ramble. Not saying this is your situation. Just something to think about… Not every bike can be made to fit you…hence the slowtwitch motto…‘buy the bike that fits’
Andy
This is a simple problem with very simple solutions
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when you wobble dont brake, go faster it will straighten you out. This sounds like suicide but if you brake when you wobble you increase friction on your wheel and increase chance of wobble, speed out of the wobble and you will increae stability and survive.
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tighten your head set
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tighten your kewers
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put the correct pressure in your tires (at least 130 clinchers)
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dont wuss out, your bike can go faster than you think it can. I used to have an old cannondale that would go 33mph on flats and upward of that on ths decents, its an aluminum frame and on the rikkety old roads in california here my nuts will never forgive me!
glyn
I second the motion for checking your headset. I had a wobble issue when I first got my P3 and it turned out to be a loose headset. Also, 29 mph isn’t deadly fast. I flipped over one of my training partners at 28mph and lived to tell about it. 
Good luck,
Mike
Check your headset - it should be tighter than you think…
*You should be able to ride with a headset loose enough ,to ride with no hands .Most do the “front brake locked” check ,*rock back & forth to see upper bearing cup play on the headset, one hand on the headset ,one on the brake (locked wheel )
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