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First speed wobble crash

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First speed wobble crash

Old 09-24-20, 10:34 PM
  #76  
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This is Chloe Dygert's horrific crash today in the UCI world time trial


Is that a speed wobble as she goes into the turn and loses control? Or something else?

No word yet on her injuries.
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Old 09-24-20, 11:14 PM
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Originally Posted by MinnMan View Post
This is Chloe Dygert's horrific crash today in the UCI world time trial

Is that a speed wobble as she goes into the turn and loses control? Or something else?

No word yet on her injuries.
To my eyes that is a speed wobble and similar to mine, though I didn't go over a guard rail and have the injuries she did. Most other speed wobbles that have video tend to be in straight sections of road and you can try and ride it out. Much tougher to do when coming out of corner. I hope her recovery is swift but last news said she had surgery to repair lacerations in her leg. That was a tough clip to watch.
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Old 09-25-20, 07:55 AM
  #78  
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Originally Posted by blakcloud View Post
To my eyes that is a speed wobble and similar to mine, though I didn't go over a guard rail and have the injuries she did. Most other speed wobbles that have video tend to be in straight sections of road and you can try and ride it out. Much tougher to do when coming out of corner. I hope her recovery is swift but last news said she had surgery to repair lacerations in her leg. That was a tough clip to watch.
Yes, hard to watch. I feel badly for her - 23 y.o, American world champion time trialist, and now this.

The thought of taking a fast downhill curve and then losing control like that.....

There was a lot of talk earlier in this thread about causes of speed wobbles and whether the culprit is the bike, the rider, etc., but here was a professional rider and a bike surely set up by pro mechanics....
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Old 09-25-20, 11:16 PM
  #79  
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https://cyclingtips.com/2020/07/bicy...-to-stop-them/

I've experienced it hands off, never hands on. Most recently in my new Fog Cutter build.
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Old 09-26-20, 12:18 AM
  #80  
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Originally Posted by MinnMan View Post
I just don't think that I'd have the guts to "relax" my grip if I were experiencing that. So, what to do? Move the knees inward, try to pedal, and what about the upper body? Probably if I'm going that fast, I'm already down and tucked. And no brakes, I assume, however tempting?
You still need to brake if approaching a sharp turn.

Squeezing the top tube with your knees or hips is a very good start, followed by relaxed grip on the handlebar (using your core muscles to support your upperbody weight), and finally, putting more weight on the front wheel by crouching down real low.

You may also need to do some adjustments to the seat to help relieve some pressure off your arms to help you hold the handlebar with less pressure.
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Old 09-26-20, 02:15 AM
  #81  
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yikes...maybe it was a "shiver shimmy"...didn't seem like she was going that fast. there have been a few occasions where my front/upper half got cold on a descent
and the resulting shimmy is nearly the same as when i'm not cold and get mechanical shimmy on a decent. hmmm....sensing a new thread...cold shimmy vs mechanical shimmy...
they are both horrible and definitely potentially crash-inducing.
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Old 09-26-20, 12:03 PM
  #82  
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Originally Posted by cubewheels View Post
You still need to brake if approaching a sharp turn.

Squeezing the top tube with your knees or hips is a very good start, followed by relaxed grip on the handlebar (using your core muscles to support your upperbody weight), and finally, putting more weight on the front wheel by crouching down real low.

You may also need to do some adjustments to the seat to help relieve some pressure off your arms to help you hold the handlebar with less pressure.
Another response that seems to help is taking weight off the saddle, onto feet as well as upper body. Not out of the saddle, just less weight.
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Old 09-26-20, 04:06 PM
  #83  
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Originally Posted by MinnMan View Post
This is Chloe Dygert's horrific crash today in the UCI world time trial

https://twitter.com/sporza_koers/sta...36302474956804

Is that a speed wobble as she goes into the turn and loses control? Or something else?

No word yet on her injuries.
sure looks like it is to me. She looked like she hit either a road imperfection or something on the road when the bars jump. Thatís a classic ďimpulse responseĒ from control theory and it looks to me like it set up either an under damped or resonant response in the frame. That would be right in like with what I was saying prior. An impulse like that contains many high frequency components - actually many of all frequencies - of which some were at a sensitive part of the frames frequency response and an oscillation starts.

itís an excellent example both of how any bike is susceptible and how it can become uncontrollable for even the best riders.

thoughts and prayers out to Chloe. One of my favorite riders. Hoping for a quick and complete recovery.
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Old 09-26-20, 04:12 PM
  #84  
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I agree - it looks like the initial "jerk" came from a small corrugation in the road - one almost too small to see.

Originally Posted by JohnJ80 View Post
sure looks like it is to me. She looked like she hit either a road imperfection or something on the road when the bars jump. Thatís a classic ďimpulse responseĒ from control theory and it looks to me like it set up either an under damped or resonant response in the frame. That would be right in like with what I was saying prior. An impulse like that contains many high frequency components - actually many of all frequencies - of which some were at a sensitive part of the frames frequency response and an oscillation starts.

itís an excellent example both of how any bike is susceptible and how it can become uncontrollable for even the best riders.

thoughts and prayers out to Chloe. One of my favorite riders. Hoping for a quick and complete recovery.
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Old 09-26-20, 04:15 PM
  #85  
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"As she approached a turn, she flipped over a guardrail. Jim Miller, USA Cycling's chief of sports performance, said she had a "speed wobble" going into the turn and lost control. "

https://www.indystar.com/story/sport...er/3534525001/
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Old 09-26-20, 05:08 PM
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I hit a guardrail at about the same angle and speed last October, resulting in a deep leg laceration. Guardrails are not human friendly.

Good to hear a full recovery is expected.
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Old 09-26-20, 05:32 PM
  #87  
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Originally Posted by Carbonfiberboy View Post
Yeah and then the guy goes right back to doing wrong again. Just asking for it.
Responding to an older thread, i just saw it. what exactly did he do wrong that is is asking for it? I saw him take his right foot off the pedal and lower it, recover, then put it back on. that was all.

i was in a high speed wobble once, right over the bars, and the my face lost against the road, (not to worry, i am still handsome). no helmet then, not that it would have helped, that was long ago.

now when descending i have learned to continuously pedal. here where i live there always seem to be winds of some sort and i find peddling vs not peddling gives me much more stability. i will even break while peddling just to maintain stability, sometimes those winds are really strong and seem to come out of no where.
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Old 09-26-20, 05:55 PM
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Originally Posted by spelger View Post
Responding to an older thread, i just saw it. what exactly did he do wrong that is is asking for it? I saw him take his right foot off the pedal and lower it, recover, then put it back on. that was all.

i was in a high speed wobble once, right over the bars, and the my face lost against the road, (not to worry, i am still handsome). no helmet then, not that it would have helped, that was long ago.

now when descending i have learned to continuously pedal. here where i live there always seem to be winds of some sort and i find peddling vs not peddling gives me much more stability. i will even break while peddling just to maintain stability, sometimes those winds are really strong and seem to come out of no where.
Did not raise his butt off the saddle, leveling his pedals, did not put a death grip on his TT with his knees. He could have gotten lower in the drops, moved his butt forward a bit and weighted his front wheel more, too. I'll drop the outside pedal for sharp corners, but then I'm going more slowly. For sweepers, I keep 'em leveled. Evening your weight distribution makes the bike more stable as does getting more aero. I'll wind check sometimes coming into corners, but mostly I brake and hold my position. I also never stick a knee out, but rather keep the inside knee pressed against the TT and use it to steady the frame and control lean to some extent.
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Old 09-26-20, 05:59 PM
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Originally Posted by MinnMan View Post
I agree - it looks like the initial "jerk" came from a small corrugation in the road - one almost too small to see.
I stepped through this slowly trying to get frame by frame. What you see is that she has her weight down in a tuck and the saddle is relatively lightly loaded. As she gets the impulse input, you can watch the seat atop the seat tube start to oscillate and the amplitude increases with each wobble. So this was a resonance issue and not an underdamped situation. That is a serious frame design problem and the fault of the frame. As she makes that carved turn, she has her right knee pointed toward the center of the radius she's circumscribing in her turn. If she could have brought that knee back to the top tube, that *might* have helped her regain control but I suspect it was the rear triangle of the bike that was in resonance. At any rate, as she was carving the turn she was loading up the rear triangle and that's the energy that is provided the oscillation.

Bottom line here, I don't think there is anything she could have done to get this back under control. You can see her stand up a bit from the seat as she hits the thing/dip in the road probably pitching her slightly forward. That unloads the seat more and removes any damping she might have been able to provide. Any change in her side to side body position (knee in, etc...) would have caused her radius to decreased and there would have been insufficient time and space to get it under control. She would have just crashed in a different place. Her efforts to try and correct the steering probably just added delay to the steering which would translate into a phase shift in the frequency domain and probably made it more unstable.

So, I'd hang this one solidly on the frame manufacturer (Felt?) not on Chloe. This also dramatically and sadly puts the lie to the comments made earlier that modern frame designers and their designs have eliminated the problem. They haven't and she's proved that with this crash. Furthermore, it's fair to stipulate that she's among the best bike handlers alive with one of the best maintained state of the art bikes around and it damn near killed her. If I'm not mistaken, she rides on FELT frames. They have a little engineering soul searching to do. This turn was not something that was out of reach for speed or terrain by recreational amateur enthusiasts and I'm sure it's a stock frame of their best build.
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Old 09-26-20, 06:11 PM
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Very interesting and educational - particularly as I ride a Felt (though a 2011 model, maybe not the same design, and also I assume she was riding a TT bike?)

Can you clarify the three statements that I've bolded? If her weight on the saddle is reduced and she's moving her weight forward, how is she loading the rear triangle?

Originally Posted by JohnJ80 View Post
I stepped through this slowly trying to get frame by frame. What you see is that she has her weight down in a tuck and the saddle is relatively lightly loaded. As she gets the impulse input, you can watch the seat atop the seat tube start to oscillate and the amplitude increases with each wobble. So this was a resonance issue and not an underdamped situation. That is a serious frame design problem and the fault of the frame. As she makes that carved turn, she has her right knee pointed toward the center of the radius she's circumscribing in her turn. If she could have brought that knee back to the top tube, that *might* have helped her regain control but I suspect it was the rear triangle of the bike that was in resonance. At any rate, as she was carving the turn she was loading up the rear triangle and that's the energy that is provided the oscillation.

Bottom line here, I don't think there is anything she could have done to get this back under control. You can see her stand up a bit from the seat as she hits the thing/dip in the road probably pitching her slightly forward. That unloads the seat more and removes any damping she might have been able to provide. Any change in her side to side body position (knee in, etc...) would have caused her radius to decreased and there would have been insufficient time and space to get it under control. She would have just crashed in a different place. Her efforts to try and correct the steering probably just added delay to the steering which would translate into a phase shift in the frequency domain and probably made it more unstable.

So, I'd hang this one solidly on the frame manufacturer (Felt?) not on Chloe. This also dramatically and sadly puts the lie to the comments made earlier that modern frame designers and their designs have eliminated the problem. They haven't and she's proved that with this crash. Furthermore, it's fair to stipulate that she's among the best bike handlers alive with one of the best maintained state of the art bikes around and it damn near killed her. If I'm not mistaken, she rides on FELT frames. They have a little engineering soul searching to do. This turn was not something that was out of reach for speed or terrain by recreational amateur enthusiasts and I'm sure it's a stock frame of their best build.
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Old 09-26-20, 06:27 PM
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Originally Posted by MinnMan View Post
Very interesting and educational - particularly as I ride a Felt (though a 2011 model, maybe not the same design, and also I assume she was riding a TT bike?)

Can you clarify the three statements that I've bolded? If her weight on the saddle is reduced and she's moving her weight forward, how is she loading the rear triangle?
Sure, I think I can.

I should be clearer on the frame thing - it could also be an imperfection in the layup but the geometry is ok. At any rate, I doubt the Felt engineers did any actual testing of frequency response of the frame design in general but certainly not of her frame in particular. This turn didn't look all that special or difficult to me as a amateur rider but certainly not that special to a world class cyclists like Chloe. Bottom line here, I think Felt owns this problem. If I were her, I wouldn't get on that design again unless they could show me they found and fixed the problem and then I'd want them to do some frequency testing of the exact frames/bikes they were planning on giving me. It's either in the design or in the layup.

To your bolded points:

1. "has her weight down in a tuck and the saddle is relatively lightly loaded". She's on her aero bars and the very front of her saddle as she enters the turn. Her outside leg is straight, pressing down hard on the pedal, and her knee is pointed into the turn to allow her to lean the bike. Her tires aren't sliding, they're anchored to the pavement by sufficient friction. So the seat has less weight on it than it normally would if she were, say, riding with her hands in the drops or on the shifters. What that does, in my opinion, is free up the seat end of the seat tube and rear triangle to oscillate. Had she been sitting on the seat with more weight and farther back, she would have anchored that end. The lower end is the stiffest part of the bike in the bottom bracket and I doubt that can oscillate much.

2. "as she was carving the turn she was loading up the rear triangle". Even though she's not sitting on the seat, her weight is carried by the frame and ultimately the tires. She's pressing down hard on the outside pedal to put as much weight as she can as low between the two wheels as she can. The bike wants to straighten up but she's holding it down and by controlling the front wheel and her CG, she's forcing the bike around the radius. That puts stress through the back triangle and loads it up. But, because she's not really pressuring the seat or even not at all briefly, all that energy is available to "spring" out of the frame and provide the energy to oscillate the top of the seat tube and, I would presume, the top tube. Because of her right knee being used to help her turn, she can't clamp it to the top tube or the bike would straighten up somewhat and she'd miss the turn and run off the road. So between the two, it looks to me like she was either going to crash where she did or slightly farther through the turn but it looks like she was kind of cooked when she hit that dip/thing and she had no room or time to recover.

3. "You can see her stand up a bit from the seat as she hits the thing/dip in the road probably pitching her slightly forward. That unloads the seat more and removes any damping she might have been able to provide. " I can't see what she hit from the video or the imperfection in the road, but there was something there. You can see if you step through it, she gets pitched slightly forward suddenly, and from my viewing, it looks like she comes off the seat even more (i.e. nose of saddle). This would make the lightly loaded end of that "tuning fork" even more able to oscillate. That's when the oscillations rapidly grow in amplitude if you watch the side to side movement of the saddle - it gets wider and wider until she goes over the edge.

to the weight on the seat issue - of she had been sitting on the seat more solidly so in essence she had equal weight on her pedal and her seat, that effectively changes the frequency of oscillation of that seat tube to be probably twice as high. Thatís important because that means it is likely out of the resonant frequency range and because itís going to be harder to get something as gross as a CF seat tube with a 120lb damper on it to oscillate at that higher frequency. But if one end is unweighted and all the weight is on one end, itís kind of like you holding a tuning fork by the end - it will still oscillate when you whack it.

I'm an electrical engineer so I'm a little out of my league here on mechanical resonance, but the signs all seem to be there. The math is the same whether it's electrical or mechanical.

J.

Last edited by JohnJ80; 09-26-20 at 06:52 PM.
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Old 09-26-20, 06:50 PM
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Man I did not need to see that. Have a Felt DA for sale now lol.

Not to entirely derail the thread but I had just read this article the day before Chloe's crash. Have to say I agreed with it at the time, more so now.

https://pezcyclingnews.com/features/...inst-tt-bikes/
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Old 09-26-20, 06:57 PM
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I've raced bicycles and motorcycles, and experienced these wobbles a lot, on motorcycles it is often called the "death wobble."

It is important that your wheels be true, that the frame is properly aligned, and that the hubs are precisely centered in the dropouts. The front wheel should be balanced.

How to you balance a front wheel? By using a cycle computer, the kind which uses a magnet clamped to one of the spokes. Put your bike upside down, your front wheel will usually turn by itself until the heaviest part is pointed downwards. Attach the cycle computer magnet opposite the heavy side. Then spin the wheel. If the wheel stops with the magnet on the low side, move the magnet along the spoke toward the hub, the closer to the hub it gets, the less weight is felt at the rim. Ideally, when you spin the front wheel, it should never stop in the same place twice.

You can also use tape weights on the rim or spoke nipples, but as I use a cycle computer, I like the method I described above, and it also allows for very fine balancing.
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Old 09-26-20, 07:20 PM
  #94  
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Not clear what the result of this was, but it's possible she had a last minute bike swap?

https://www.cyclingnews.com/features...me-trial-bike/
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Old 09-26-20, 07:22 PM
  #95  
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I'm regretting not starting a new thread about the Dygert crash. We kind of have two different threads overlapping one another.
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Old 09-26-20, 08:14 PM
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Originally Posted by downtube42 View Post
Another response that seems to help is taking weight off the saddle, onto feet as well as upper body. Not out of the saddle, just less weight.
If you use your core muscles to unload your arms durind downhill coasting, it will also unload the saddle by over half the weight.

If you simply pushed on your feet to try to take some of the weight off the saddle, you may or may not relieve some of the pressure from the arms so using the core muscles is a better approach to the same goal. This also requires adjustments to the bike's setup to work - you must be able to take your hands off the bars in the normal riding position without falling backwards or forward, perfectly balanced.

Skip to 8:06 minutes into the video. You can also do the same thing while coasting (in fact, it's a lot easier to do it while coasting).


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Old 09-26-20, 08:18 PM
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Originally Posted by cubewheels View Post
If you use your core muscles to unload your arms durind downhill coasting, it will also unload the saddle by over half the weight.

If you simply pushed on your feet to try to take some of the weight off the saddle, you may or may not relieve some of the pressure from the arms so using the core muscles is a better approach to the same goal. This also requires adjustments to the bike's setup to work - you must be able to take your hands off the bars in the normal riding position without falling backwards or forward, perfectly balanced.

https://youtu.be/gbFrz5FsIow?t=488
If you take your hands off the bars during a speed wobble, you might be a ninja. Can't imagine many people would dare.
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Old 09-26-20, 08:28 PM
  #98  
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Originally Posted by MinnMan View Post
If you take your hands off the bars during a speed wobble, you might be a ninja. Can't imagine many people would dare.
LOL, don't! Not sure if you are kidding or serious but the video I posted is to demonstrate good bike fit, not getting out of speed wobble!

A good fit is the first step in avoiding speed wobble.
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Old 09-29-20, 07:10 AM
  #99  
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Velonews just publish a piece about the Dygert crash
https://www.velonews.com/gear/tech-w...nt-end-wobble/
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Old 09-29-20, 12:23 PM
  #100  
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Originally Posted by esskay1000 View Post
Velonews just publish a piece about the Dygert crash
https://www.velonews.com/gear/tech-w...nt-end-wobble/
Not just Velonews, but Lennard Zinn. He focuses on front end wobble. Interested to hear JohnJ80 's take on this.
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