Speed Wobble

X2.....http://www.cyclingtips.com.au/2011/03/speed-wobble-when-the-bike-shakes-its-head/

holy crap...that video in that link was nuts!!! 

As someone who has gone over the bars 2 times (and don't wanna any more), I would absolutely cr@p my pants if that happened to me.

It's only happened to me a few times and since I'm too old to hurt myself I rarely go faster than 30-35 even if it means riding the brakes pretty hard.  I have to hand it to the rider in that video as he obviously knows what he is doing.

It's the last climb/desent in and out of the south part of Auburn on Auburn Folsom Road from Indian Hill down to the Shirland Tract corner. Strangely enough if you look on YouTube there is an "Auburn Folsom Road Speed Wobble" video (http://youtu.be/QIcxgj_DGEk) in the exact spot mine occurred. We ride from the Rancho Cordova Fish Hatchery to Beal's Point then up to King Rd across to Loomis, then to Old Town Auburn and loop around coming down Auburn Folsom. Tough ride that I used to look forward to this long descent, but will do so a bit more cautiously in the future.

I never would have imagined this could happen.

Does it only happen in high-speed descents (over 30-35 mph)?  And does it usually start when you change position (like you got out of aero, or if on a road bike you move from the hoods to the drops)?

ETA:  Thanks for sharing this, and glad you came out of it unscathed!

Edited by chayes 2013-04-08 10:35 PM

I would crash for sure.  I never go fast enough for this to happen!

Below is a post from Slow Twitch on the subject that seems fairly well informed. The Hwy 267 n. Shore Rd is definitely another long descent that I'd be more conservative on...it also happens to be part of the IM Lake Tahoe that will be descended twice. Will be interesting to see if there are any shimmy post race reports where everyone will be going all out race speed...Re: High Speed Wobble w/Aero Wheels [tritiger] [In reply to] Quote | ReplySPEED WOBBLE When a customer brings his bike into his LBS and complains of speed wobble (death wobble, front-end shimmy) often the typical bike shop mechanic immediately starts farting around with the headset adjustment. There is no adjustment problem, nor are the wheel bearings loose, and in fact it is most likely that nothing is wrong at all. Speed wobble is just an inherent "flaw" of bicycles. Bicycle frames are amazingly stiff and strong in a vertical plane, but horizontally they are not. They are like ladders, and when you stand on a ladder it is strong, but when you and a friend stand a distance apart, each of you grasping one end of the ladder, and you twist, the weakness of the ladder is apparent. In that same way, when a bicycle is moving in a line straight ahead, and gyroscopic effects of the wheels weigh on a unit as elastic as a bicycle frame—with its fork and wheels—you might get shimmy. Shimmy occurs at a certain speed, depending on the bike and the rider. I have heard it said that every bicycle is prone, depending on its geometry, materials, and rider position, a particular resonant frequency, at which the bicycle oscillates. All that occurs when a given speed is reached on a descent. The shimmy will stop if the rider unloads the saddle, because the mass of the rider is the anchor about which the oscillation operates. It may also be helpful to place the inside of your leg against the top tube on a descent when you experience a shimmy. Certain elements will make the bicycle more prone to oscillation. All other things equal, those elements that render the bike more elastic will aid in its ability to shimmy. Therefore, a longer head tube will make the bike more likely to shimmy. Lighter, thinner tubes will make the bike more prone to shimmy. I suspect that shimmy might be more prominent now than in days past because bikes are so light, and their components somewhat more susceptible to lateral flex. Shimmy is more likely in cold conditions, or when a rider is nervous and grips hard on the bars, because the vibration of a shivering rider is roughly similar to that of a frame's shimmy frequency, and this can help bring on the shimmy. Therefore, while speed wobble is disconcerting, if you can adopt the habit of unweighting the saddle during a long, straight descent any shimmy problem should be largely abated.- Dan Empfield, here quoted. I've lowered my aerobars, thus shortening the effective head tube height. Seems to help a bit. I may go lower at MT because I'll be spending quite a bit of time climbing anyway. At least I hope I'm climbing and not stopped!