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Speed Wobbles !

Old 06-03-22, 09:07 PM
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Bendopolo
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Speed Wobbles !

The second half of my standard ride includes a relatively steep 1/2 mile steep grade. I hit 42 mph on it for a short distance on my Cannondale FSI.. Today I was ripping along in the Bike lane going down this grade as I have for 100 times. A School Bus flew by me just far enough away that I heard the mirror fly by my head. Suddenly my front wheel seemed to come alive and start wanging all over. At first I thought I blew a tire or lost a spoke. I was flying over the ground, prospects dim. I don’t know if the bike was shaking my head or the wheel lost its integrity. The rim seemed to be snaking all over. I just struggled to stay up, while flying down this hill, with a Bus as close as 24 inches away. I had no control of my bike, I knew better than to brake, the hill was steep enough that I wasn’t slowing down. The rear wheels of the Bus came spinning by me and I was ready to jump off if it got any closer. Finally the rear end of the Bus went by and I leaned back to try to take some weight off the front tire. I clamped the Frame with my legs. The combination of the two settled the bike. I glided down, slowly braking with my rear wheel, all the time repeating “Oh **** Oh ****””. I got stopped and sat on the curb for a minute. I looked that Bike all over and everything seemed solid so I rode it home. I couldn’t make it happen again and the front end was solid as a rock. I took it to my shop and they determined that the front wheel needed to be trued. Everything else seemed to be fine. We discussed a new front tire and although my front only had about 3 months on it, and I’m going to change it out just to be sure. Seriously the scariest thing I’ve been through on a Bicycle.

Last edited by Bendopolo; 06-07-22 at 07:49 PM.
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Old 06-03-22, 09:47 PM
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I’ve survived a dreaded “tank slapper” incident before, in almost the very same situation as you: bombing a hill at 40+ mph, when some unknown force started the front wheel oscillating out of balance. Could have been the wind, an errant slipstream from a passing car, uneven pavement, or just some small steering aberration, but it was terrifying. To my knowledge, it had nothing to do with the bike itself; subsequent descents of the same stretch of road went off without a hitch.

You tell a great story, by the way. Glad you lived to tell it!
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Old 06-03-22, 09:49 PM
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Glad you survived to tell the tale. High speed wobbles can truly be terrifying. Super that you got it sorted so quickly.
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Old 06-03-22, 10:14 PM
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I think of speed wobbles as being caused by out of true wheels, and they normally aren't very large. What you described sounds more like a slight imbalance that quickly oscillates out of control, which can be super sketchy and annoying. I doubt a speed wobble would have affected you the way it did, and I doubt trueing the wheel will fix the problem; When this happens to me I clamp the top tube with my knees. Never happened to me at that speed, personally I would just find another bicycle if mine did that to me. Its really not worth crashing at that speed

Last edited by LarrySellerz; 06-03-22 at 10:46 PM.
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Old 06-03-22, 10:40 PM
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Unmentioned but important. Last week I had a front spoke replaced. So a front truing was important. It has never happened before and I ride that area often. Lastly, I have over $5000 into this Cannondale FSI 2 with ceramic bearings and oval front sprocket,It has been a fantastic bike. Not going to chuck it just yet. Never been crashed, and dream to ride. Speed wobbles with a Lefty Fork…Terrifying
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Old 06-03-22, 11:15 PM
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My wheels are slightly out of true, tires are 2 years old and did a sloppy job sitting the tires. Additionally, the two wheels are out of alignment with the frame twisted ever so slightly due to past accident with the bike.

I've ridden the bike downhill a lot of times >40 mph and never once had wobble in those descents. I assume a crouched down low position with hands on the drops, elbows bent at a right angle, and knees gripping the top tube. I'd also be sitting at the back edge of the saddle in case of emergency braking, I won't flip over.

However, I'd caution sitting too far back on the saddle. The bike feels unstable if you're sitting too far back. The front wheel feels eager to turn on its own.

The ONLY time I ever had wobble was carrying too much groceries in weight and I could actually feel the frame flexing underneath me when pedaling. Fortunately the wobble occurred at a low speed, at 12 mph and I was able to stop without any difficulty.

So I'd possibly wager a heavy rider on a bike that flexes quite a bit??
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Old 06-04-22, 07:02 AM
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Originally Posted by LarrySellerz View Post
I think of speed wobbles as being caused by out of true wheels, and they normally aren't very large. What you described sounds more like a slight imbalance that quickly oscillates out of control, which can be super sketchy and annoying. I doubt a speed wobble would have affected you the way it did, and I doubt trueing the wheel will fix the problem; When this happens to me I clamp the top tube with my knees. Never happened to me at that speed, personally I would just find another bicycle if mine did that to me. Its really not worth crashing at that speed
That may be how you think of speed wobble, but the general term refers to the frame going into resonance like happened to the OP. This has been discussed at great length in the research. The resonance can be triggered by all sorts of things. Some bikes resonate easily, and some never do. The on-ride fix is to clamp the top tube with the knees. It changes the resonant frequency of the bike. It was VERY unlikely that a slightly out of true front wheel or a new tire was the fix for this.
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Old 06-04-22, 07:34 AM
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@Bendopolo , Typing as scientifically as possible with only an innerweb degree in fluid dynamics, I would say that if the bus sped past you fast enough for you to hear the mirror, it was pushing a big huge ball of pressurized turbulence ahead of it giving you a burst of it as it went by and you probably unconsciously corrected for that using madd skillz on an awesome bike and that's what set up the resonance in your frame. Kudos for not dying.
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Old 06-04-22, 07:58 AM
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+1 The combination of the bus passing by you so closely, as the previous post said, may have created some crazy wind turbulence that made the front wheel lose it's balance.

I've bombed down hills at the same speeds with all of my bikes over the years but never experienced what the OP did. Normally when I ride I grip the handle bars firmly but not tight so my hands and arms don't get tired. However, for steep downhills, I have a pretty tight grip on the drops and both of my hands are pretty far forward into the curve of the bars with the top of my forearm pinned against the top of the bar. I don't know if this is the "correct" position or not but that's what I do. My feet are also horizontal in the crank so I don't have more drag on one side versus the other, and I'm in a deep tuck.
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Old 06-04-22, 08:19 AM
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I felt the wave. Possible overcorrection? I’m not a “Flinchy Rider” usually. I gave it a good hard try on the way home but could’nt recreate it at slower speed.
Anazing the speed I picked up as the Bus passed. I was in a tight corridor of, Wall, Bike Lane, Bus a foot over the line. Lessons:
Don’t brake.
Take weight off the front.
Clamp Frame with legs
Stay centered and ride where the bike is going, you can’t steer, only “influence” your direction with your body.
I still Skateboard, does tons for your balance. But I think it was more luck than anything. I had visions of Road Rash dancing in my head.
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Old 06-04-22, 08:26 AM
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Originally Posted by KerryIrons View Post
That may be how you think of speed wobble, but the general term refers to the frame going into resonance like happened to the OP. This has been discussed at great length in the research. The resonance can be triggered by all sorts of things. Some bikes resonate easily, and some never do. The on-ride fix is to clamp the top tube with the knees. It changes the resonant frequency of the bike. It was VERY unlikely that a slightly out of true front wheel or a new tire was the fix for this.
My thoughts exactly. I have worse wheel condition than the OP.

The only time I ever had wheel wobble when I was hauling a heavy load and I can feel the frame flexing. I suppose the frame flexing can trigger the resonance, w/e and I think it's the side-to-side flex that triggers wobble. In addition to squeezing the top tube with the knees another widely known way to prevent or stop wheel wobble is shift your weight to the front. Another thing is to lower your CoG. Drop yourself down and get stable and aero too.

I think for big riders, the frame would be flexing quite a bit. For those who are dying to find a reason to buy another bike, then buying a bike with stiffer frame design would be a good reason. Disc brake bikes tends to be built with stiffer frame, particularly the fork. And then Thru-axles reduce flexing between the axle and the frame or fork. If tight on budget, then practice hunching down on fast descents and possibly losing weight.
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Old 06-04-22, 09:33 AM
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You may want to contact bus company and complain about driver.
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Old 06-04-22, 11:00 AM
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Originally Posted by LarrySellerz View Post
I think of speed wobbles as being caused by out of true wheels, and they normally aren't very large. What you described sounds more like a slight imbalance that quickly oscillates out of control, which can be super sketchy and annoying. I doubt a speed wobble would have affected you the way it did, and I doubt trueing the wheel will fix the problem; When this happens to me I clamp the top tube with my knees. Never happened to me at that speed, personally I would just find another bicycle if mine did that to me. Its really not worth crashing at that speed
What the OP described is a speed wobble. What you described is not.
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Old 06-04-22, 12:20 PM
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Sounds like your speed wobble was caused by aerodynamics, since there was a bus going by, he was pushing a lot of air in your direction. And the wobble stopped after the bus went by so….yeah. The gust from the passing bus probably started the wobble and once it starts, it’s hard to stop it!
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Old 06-04-22, 01:20 PM
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In 30+ years of riding, I’ve had it a few times.

Each of those times was a descent with strong wind. It’s rare, and it’s not predictable but it’s pretty awful when it does happen.

No question in my mind that the bus caused this. Isn’t riding in traffic fun?
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Old 06-04-22, 02:11 PM
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Turbulent air got you. Dirty, or turbulent, air does bad things to bikes, motorcycles, race cars, sailboats, planes, etc.

Last edited by Mojo31; 06-04-22 at 04:04 PM.
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Old 06-04-22, 03:27 PM
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You tensed up, that's all.
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Old 06-04-22, 04:15 PM
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I'm not sure I want to do 50 mph on a mountain bike. Especially aCannondale F-Si.

Road bike, no issue. But wide tires on a mtn bike it seems like there'd be some issues with the tread not staying in line with the rim as well as it should due to the larger area of the sidewalls and less support from the lower pressure in wide tires.
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Old 06-04-22, 08:48 PM
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I've experienced wobbles on bikes and motorcycles, and they can be scary. They are a kind of gyroscopic thing in which destabilizes the wheel when it tries to move to a different phase. Wheels spin smoothly in equilibrium when they are perfectly vertical or horizontal, if they are anywhere in between these positions they try to push back to equilibrium, in certain situations they fluctuate between phases. The effect amplifies itself as the wobble increases. To minimize the potential for this problem, keeping the wheels true and in balance is important. Another possible cause is fork/frame misalignment, or a loose headset.

You can balance the front wheel with a cycle computer magnet which attaches to a spoke. Normally when you spin the wheel, it will stop with the heaviest side down. Attach the magnet to a spoke opposite to the heavy side. Moving the magnet closer or further away from the hub can fine tune the balance. When the wheel is balanced, it should stop turning in random positions. Heavy grease in the headset and tightening the bearings enough to add a little resistance when turning the fork can help. Motorcycles use dampeners and/or stabilizers for the same effect.
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Old 06-04-22, 09:07 PM
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Originally Posted by tomato coupe View Post
You tensed up, that's all.
This could be the culprit. Tensing up when the bus went by could do it. When I was racing my bike, a well maintained Peugeot PX10, would get into a wobble on descents, especially when riding with other riders surrounding me. We changed a lot of parts, including a Spidel roller bearing headset. What we finally found was that I was tensing my back and shoulders, and probably gripping the bars harder. Once I learned this and relaxed more it eliminated the wobble. My bike was a 62 cm, 531 Reynolds frame, and had a lot of flex.

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Old 06-04-22, 10:49 PM
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Originally Posted by Rolla View Post

You tell a great story, by the way. Glad you lived to tell it!
Yeah this ^^^

Glad you are ok. I doubt I would have been so lucky.
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Old 06-05-22, 01:10 AM
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Originally Posted by 50PlusCycling View Post
keeping the wheels true and in balance is important. Another possible cause is fork/frame misalignment, or a loose headset.
I have all these "problems" on my bike except for loose headset but no speed wobble at >40 mph. I absolutely agree about a loose headset causing speed wobble, I have quite a few experiences with that.

I strongly doubt an "up and down" imbalance will cause speed wobble. However, a lateral or "left and right" imbalance might actually cause speed wobble. But the much narrower and lighter wheels of bicycles even MTBs compared to a motorcycle wheel would make that effect negligible.

I'd bet that most cyclists have their wheels out of balance. Even on a perfectly trued, and perfectly balanced rims would lose balance as soon as you mount tires on it due to imperfections on the tire. This is why when you buy new tires for your car, the shop would also balance your wheels because the new tires would imbalance the wheel. But no one bothers to put weights on their spokes to balance their wheels on their bicycles. It would be extraordinarily rare because the side effect of an imbalanced wheel on a bicycle is negligible.

On a motorcycle wheel with much wider wheel proportions and much heavier too then yes, the lateral imbalance would have a greater effect.
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Old 06-06-22, 05:04 AM
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This is a problem with bike design that nobody is talking about, the trend to market road-bikes with more sporting geometry that makes the bikes twitchy.

There is really Zero reason for a road-bike to have to steer very quickly. A mountainbike going slow in tight trails has a lot more use for quick steering geometry, but a road-bike, on roads designed for multi-ton motor-vehicles, is never going to run into turns so tight that it has to have the ability to turn any more quickly than those motor-vehicles because it is almost always going to be going much slower than they are on the same roads, get it ???

But instead of making road-bikes that are very stable, they make them very quick-steering and twitchy, and on top of the quick geometry they are making the frames as light as possible so they are not going to be as stiff as they would be if they had more material in them, and the result is the higher the speed, the less safe they are to ride.

An old water-pipe framed Schwinn Continental with very laid-back steering tube geometry, which would give it a lot of "trail", will handle better at high speed than a modern bike with "racing" geometry. Also heavier wheels are more stable at speed due to the gyro effect, super-light wheels do nothing but help in the first few car-lengths of acceleration, after that they have no advantage over a heavy wheel in most riding. And of course the fashion trend to sell non-pros "aero" handlebars used in time-trials, which give much less control than standard drop-bars, also make it hard to control a bike in an emergency.

I am sure a number of cyclists have been killed or maimed after losing control at speed on what is being sold today as a "performance" road bike.
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Old 06-06-22, 06:51 AM
  #24  
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Since it was a school bus…as mentioned above…you should contact the school bus/student transport company, or maybe the school department (I suppose a complaint to the police wouldn’t hurt either). Give them all the info you can about the bus with regard to location, time of day, and the bus number if you happened to notice it. If you were safely on the shoulder/bike lane the bus should not have come that close to you…and/or slowed and waited until it was safe to pass you. They might be able to determine who the driver was and take appropriate action.

Dan
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Old 06-06-22, 07:10 AM
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how was the bike loaded?
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