Speed Shakes on the Bike
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2016-08-13 9:24 PM |
233 Ventura, California | Subject: Speed Shakes on the Bike
Anyone else experience these very scary moments? Where your coming up to a good clip on a downhill run and the bike starts to shimmy and grows worse very very quickly, when you grab on the binders to scrub off speed it makes it worse. When this is happening it gets so violent that you feel like your going to get thrown off the bike, until you come to a near or complete stop. Imagine coming down a mountain road at about 40+mph and having both tires go flat instantly, that is exactly what it feels like. I have had it happen on my 27yr old Peugeot at 39mph, 50mph, and 52mph. And TRUST ME, when this happens at 50+mph it will scare you so bad you will almost start to cry because the only thing going through your mind is that you are going down, its going to be horrific and your going to the hospital. One time I had a car overtaking a slower car coming up the mountain so he was coming at me in my lane head on and I had 3 feet between him and going over the cliff, the whole time the bike is violently shaking out from underneath me. So today, I was riding a new 'used' bike, 2002 Kestrel 200SC carbon bike and it happened again, this time at 45mph. Now before we all start guessing at things, here is what is fact about both bikes. 1988 Peugeot, fully reconditioned, shimano 105 group set, all bearings are cleaned, lubed and tight, headset, crankset, wheel hubs, etc. wheels trued, bontrager tubes, contitech ultra sport tires, 110psi 2002 Kestrel, fully reconditioned same as above, shimano 600/dura-ace components, Specialized S-Works tires, Bontrager tubes, wheels trued just last night before todays ride, 110psi So basically both bikes are in tip top mechanical shape so there is no reason to suspect mechanical issues. Most of these speed wobbles come on one particular down hill section of a certain road and typically with light breezy conditions. But I have had 2 other instances on other roads where this has happened. Body position is butt way back pushed past the back edge of the seat, back is long and straight, head down, lips and teeth about 2 inches from handle bar, hands on the drop bars (road bikes) with fingers extended to brake levers, grip is firm but not rigid. My goal is to hit 55mph on the Peugeot 13/53 gear ratio, I would like to get to 60+ on the Kestrel 11/53 ratio. But at the same time I don't want to get severely injured in the process. There is nothing more exhilarating then high speed downhill descents on a road bike, or a car for that matter. Anyways anyone else experience these high speed shakes that could potentially shed some light on what might be the issue or if you have had them before and how you overcame them? Its really bumming me out because it is a great way to pass lots of bikes as everyone else is scared and dragging brakes all the way down the hill. I like to hit top speeds then threshold brake late and swoop into the corner and carry as much momentum into the next leg of the bike run. Sorry I used to race cars so I have kind of carried that into my bike skill set and it feels more dangerous to be honest. |
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2016-08-14 8:33 AM in reply to: rjcalhoun |
Pro 5892 , New Hampshire | Subject: RE: Speed Shakes on the Bike A couple of things... First, make sure the bike is in perfect shape, tighten the headset, the wheels are true/round, the valve stem doesn't rattle (yes, that's enough to cause the bike to shake at high speeds). Make sure your bike fit is good, if you're too far forward, then you will experience speed shake. Finally, relax. Most common cause of speed shake is that the rider tightens up. Relaxed shoulders, relaxed grip etc will all make a huge difference. If you experience speed shake, clamp your knees on each side of the top tube and push yourself backwards, that will help to balance the bike. Then slowly brake to reduce speed. |
2016-08-14 10:27 AM in reply to: 0 |
1300 | Subject: RE: Speed Shakes on the Bike Look up speed wobble. As mentioned above, push your knees into too tube. ETA - goal of 55 mph , do you have life insurance ? Edited by Goggles Pizzano 2016-08-14 10:31 AM |
2016-08-14 11:59 AM in reply to: audiojan |
233 Ventura, California | Subject: RE: Speed Shakes on the Bike Originally posted by audiojan A couple of things... First, make sure the bike is in perfect shape, tighten the headset, the wheels are true/round, the valve stem doesn't rattle (yes, that's enough to cause the bike to shake at high speeds). Make sure your bike fit is good, if you're too far forward, then you will experience speed shake. Finally, relax. Most common cause of speed shake is that the rider tightens up. Relaxed shoulders, relaxed grip etc will all make a huge difference. If you experience speed shake, clamp your knees on each side of the top tube and push yourself backwards, that will help to balance the bike. Then slowly brake to reduce speed. I think this may come down to bike fit and form as that is the only thing that would cross over to 2 very different bikes. I have never had a 'proper' bike fitting. The bikes are in mechanically sound condition as mentioned. While I do feel like I am pushed back and relaxed I may not be similar to you 'feel' like your swim form is great, but video review shows something completely different. Also when the speed shake starts I am pretty sure that I pop upright like a panicked prairie dog as I try to reign in the speed and prepare to get launched in full panic mode. Honestly I will just have to be more mindful of being relaxed and squeezing the top tube on all my downhill descents to to make sure I have that form instead of it trying to be reactionary. Thanks! |
2016-08-14 12:13 PM in reply to: Goggles Pizzano |
233 Ventura, California | Subject: RE: Speed Shakes on the Bike Originally posted by Goggles Pizzano - goal of 55 mph , do you have life insurance ? As a matter of fact I do, 50K. I tend to put myself at risk on a pretty much daily basis, so its a smart idea to be covered. Then of course I take little risks like careening down twisty mountain roads on a bicycle. Ah the little things in life that bring us joy. Cheers |
2016-08-14 12:36 PM in reply to: 0 |
Veteran 945 South Windsor, CT | Subject: RE: Speed Shakes on the Bike I've had this happen and just commented in ST last week about this. For me, putting on my front tire when taking the bike in/out of my truck and not clamping it tight is THE most common cause of a minor 'speed shake' of the front wheel. True 'speed wobble' where the frame seems to be shaking you off, is different and downright scary. It is really an oscillation of the handlebars and front wheel. It's happened to me much more often in windy conditions with my deep dish race wheels. Cross winds that come on suddenly and strong can start it. It's happened at 40+ mph too and it will scare the crap out of you. The only answer for me is to slow down at that point. Stick one foot down (6/12 o'clock positon) while slowing. You should NOT move backwards on the seat, it will be more likely to destabilize the front wheel further. The correct thing to do is move more forward while slowing. You probably won't hit your speed goal once in a wobble, so slow down, call it a day and try again later. http://cyclingtips.com/...ike-shakes-its-head/ edited to add one more cool link https://www.youtube.com/watch?v=jW8I2hX4GSs Edited by dtoce 2016-08-14 12:45 PM |
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2016-08-15 10:02 AM in reply to: 0 |
Champion 10668 Tacoma, Washington | Subject: RE: Speed Shakes on the Bike I've only had speed wobble on two occasions. The initial time was on my first "real" road bike back in the early 80's, a Trek 560 with the stock wheels, etc. Happened just as I approached 40 mph, and scared the crud out of me. Learned the trick of clamping the top tube between my knees (to the detriment of my frame pump the first time I tried it). Later, when I swapped to a better set of wheels, the problem went away. The other time was in a time trial, aboard a custom TiCycles Softride and Specialized Tri-Spoke wheels. I'd spec'ed a Trek carbon fork (hm... Trek again) because it was lighter than the other offerings. Anyway, a hilly, long TT, and any time I got over 30mph, the front end went wild. Kinda destroyed any chance I had of posting a good time. Replaced the Trek fork with a Kestrel, and never had the issue again. The issue is that there's some harmonic at work, and you need to do something to change the frequency. Clamping the top tube does this by essentially putting a mass at the half-way point. Same with shifting weight forward or backward. Swapping to a stiffer fork can help (as above), or even a change in wheels/skewers/etc. With the Peugeot, it may just be an issue of the flexibility of the frame itself, and not much you can do to change that. Oh, and $50K for life insurance... You need more. Just sayin'. Edited by briderdt 2016-08-15 10:03 AM |
2016-08-15 3:07 PM in reply to: briderdt |
Elite 4344 | Subject: RE: Speed Shakes on the Bike This probably won't answer your question in a way that is helpful but it is the technical answer to the problem. http://rspa.royalsocietypublishing.org/content/royprsa/463/2084/1955.full.pdf Here is a recent article about Jim Papadopoulos in Nature and his quest to solve this problem. He has worked on this problem since the late 80's. He is an acquaintance of mine. This article is readable but ultimately not helpful to a rider. http://www.nature.com/news/the-bicycle-problem-that-nearly-broke-mathematics-1.20281 My Litespeed Tuscany had a speed wobble. It seems to be cured by replacing the original wheels with Zipp 101 wheels. The spokes on the original wheel were thread-like 1.5 mm. The Zipps have bladed Sapim spokes that are .9x2.2 mm. These dimensions give a much stiffer spring constant for the spoke and a laterally stiffer wheel. (The radial direction is stiffer too but that doesn't matter.)
TW
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2016-08-15 4:08 PM in reply to: rjcalhoun |
Champion 19812 MA | Subject: RE: Speed Shakes on the Bike When I belonged to a bike race team, one of my teammates was dealing with this with her new bike. The shop was trying to problem solve. What I got from this was some bikes it happens and some it doesn't. Sometimes they can figure out why but other times it is just the way the bike is and better to use another bike for descending fast. She would not race it until they solved the issue and if they couldn't fix it she didn't want the bike. I find it odd that both your bikes have this happen.....old one makes more sense to me and not so much the newer one. I'd bring the new bike back to the shop you bought it and ask them about it. Bikes aren't supposed to do this. |
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