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First speed wobble crash

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First speed wobble crash

Old 09-07-20, 11:23 AM
  #51  
shakey start
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Originally Posted by yarbrough462 View Post
Ensure your headset is properly tensioned. That will definitely cause a wobble...
Yes, what he said, plus balance the front wheel, and make sure the axles are tight.
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Old 09-07-20, 12:01 PM
  #52  
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I've had that happen on three different bikes, one on which I attained 67 years ago mph going down a mountain pass. That one was a Trek 957. 20 years later, I experienced the wobble on the same bike while on an organized tour at about 40 mph. It was me, being older and getting a little more cautious. The other two times were on a brand new 7 and a Schwinn Letour. Same thing and each time it was a long straight. Have never experience it bombing down a canyon with lots of curves. I've since learned to relax and when I start getting a little tense about the speed, slow it down.
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Old 09-07-20, 12:13 PM
  #53  
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Originally Posted by blakcloud View Post
Today I experienced a shimmy that I couldn't control. I went for a ride today and twenty minutes in I was descending a hill at 56 km and then in no time I am skidding along the pavement. The shimmy turned into a full out wobble that I just couldn't get under control.

Two weeks ago I experienced shimmy at 82 km an hour and I was able to slow the bike down and control it. I had a smaller one a few days ago at about 70 km/h. Today's was much slower but I had hit some rough pavement that may have contributed to the wobble.

Did I help contribute to this mishap, you bet I did. I didn't grab the top tube between my legs, I didn't raise my weight above the saddle or loosen my grip on the bars. These are all solutions but they are counter-intuitive when it is happening. I was hanging on for dear life, just trying to slow the bike down. I think I need to start training for this to make sure it doesn't happen again. I have done a lot of reading on speed wobble and one thing is clear, there is no definitive answer. Different solutions work for different people and the solutions are not universal. My biggest obstacle will be fear. The fear to go downhill fast again.

This is just a narrative of what happened. I was one of the unlucky ones that couldn't control today's shimmy.

The bike was the Trek Domane SL6 that is one year old exactly today.
(bold) As an experienced rider and an engineer, I agree with clamping around the top tube, although if seated, that should not be necessary assuming a seat post with greater rigidity than a wet noodle. But raising your weight above the saddle, if you mean torso, fine, but I would think you want to stay seated in the saddle to increase the lateral rigidity and mass damping of the system, to slow down the oscillations. My bike is touchy, it's a 20" wheel folder, and I have a firm grip on descents, and control my speed, I don't sail down the mountain like I used to on my Cannondale criterium racing frame. Even if it had more trail to the fork, I think with the reduced rotational inertia of the wheels, there's no way it would have the stability of a larger bike on fast descents. On the Cannondale, I've topped out the speedometer and I think it maxed at 65 kph if I recall correctly, that was 20 years ago.
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Old 09-07-20, 01:56 PM
  #54  
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Dunlop wobble & weave

I ride bikes and motorcycles. This video from Dunlop tires, in the 70s about how & why MCs wobble & weave, is quite interesting. Notably, they differentiate between wobble and weave. A big surprise was how both weight placement and size of rider makes such a difference. This could explain why some of you have recurring trouble and others do not. And why a head wind (changing weight balance) can make a difference. Since I am a new poster, this site won't let me post the site, but go to Youtube and then Dunlop Wobble & Weave.
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Old 09-07-20, 02:02 PM
  #55  
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I don't think I have seen spoke tension mentioned yet in this thread. I were having repeated wobble issues, I would want to be sure it wasn't starting with slightly loose spokes.

Prior to reading this tread, I wasn't aware that "speed wobble" was a thing. I think I experienced it a few times as a teenager and intuitively shifted my weight and clamped the top tube in the right way. I don't think anyone ever told me to do that, but still, when I make a fast descent, I often clamp the top tube with my knees (before any wobbling starts).
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Old 09-07-20, 05:23 PM
  #56  
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Originally Posted by yarbrough462 View Post
Ensure your headset is properly tensioned. That will definitely cause a wobble...
Yes, a loose headset can cause this problem.
I had the same issue. I had a cheap generic threadless headset on a steel frame road bike that I checked after a speed wobble and there was slight movement in it.
I replaced it with a Cane Creek headset which is better constructed and fits together better.
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Old 09-07-20, 06:27 PM
  #57  
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Hereís a long discussion by Lennard Zinn on bike geometry issues related to wobble and mechanical resonance.

https://www.velonews.com/gear/techni...speed-wobbles/

Worth noting here, per our previous discussion, that a number of his customers came to him with serious wobble and resonance issues on stock carbon frames. Point here is that it can happen to anyone given the right conditions in bike construction, geometry and adjustment when presented with that variance in order weight, body position, and riding conditions.

Mechanical resonance issues are tricky and very often counter intuitive to solve.
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Old 09-08-20, 06:27 AM
  #58  
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My bike Guru always told me "up fast, down slow". I'm sticking to it!
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Old 09-08-20, 07:15 AM
  #59  
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Loose headsets, wheels out of true, loose spokes, hubs, drops vs hoods, carbon resonance, tall riders, tall frames, bikes in the '80s... It seems every component is the culprit.

It's the rider. Seriously. The majority of cyclists will ride many bikes over many years and never experience this, while other riders will experience this on every bike they ride.

I've got to believe that points to either that rider's position or behavior or both.
- Position: how the bike is set up and how the rider is sitting on the bike at the time of the wobble, e.g. hoods, drops, forward, back, low, upright, etc.
- Behavior: how the rider acts and reacts to input and feedback, e.g. loose and absorb; stiff and amplify
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Old 09-08-20, 10:54 AM
  #60  
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Regardless of the specific cause in the given incident we know that speed wobble is a resonance with some kind of positive feedback that builds the resonance. (it could also be a negative control input feedback that is time-delayed just the wrong amount).

With it happening that frequently, I'd be changing anything on the bike that could be contributing. Sometimes (usually?) a lot of otherwise unrelated factors have to be just right to make it happen. Starting with tires even because that's the cheapest and easiest, but it would be a good excuse to upgrade the wheels. Handlebar width. Lube the headset. Weight distribution on the bike, tweaking the rider position.

If it's the case that control input is contributing, the recommendation that I've seen and which has worked for me is "stop fighting it". Also relax in the arms and upper body, but it needs to be almost instant.
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Old 09-08-20, 01:19 PM
  #61  
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Originally Posted by Zaskar View Post
Loose headsets, wheels out of true, loose spokes, hubs, drops vs hoods, carbon resonance, tall riders, tall frames, bikes in the '80s... It seems every component is the culprit.

It's the rider. Seriously. The majority of cyclists will ride many bikes over many years and never experience this, while other riders will experience this on every bike they ride.

I've got to believe that points to either that rider's position or behavior or both.
- Position: how the bike is set up and how the rider is sitting on the bike at the time of the wobble, e.g. hoods, drops, forward, back, low, upright, etc.
- Behavior: how the rider acts and reacts to input and feedback, e.g. loose and absorb; stiff and amplify
I have had it happen once. In my case, it was absolutely not the rider...It was a loose headset.
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Old 09-08-20, 01:56 PM
  #62  
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Originally Posted by yarbrough462 View Post
I have had it happen once. In my case, it was absolutely not the rider...It was a loose headset.
That's my point. As each rider with a wobble searches for the cause, they'll find a loose headset, loose spoke, hub issue, tall frame, carbon resonance issue...

Anyone who's ridden for only a couple years has ridden a bike with a loose spoke, loose headset, a wheel out of true, etc. A = B and B = C but A does not = C.
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Old 09-08-20, 03:21 PM
  #63  
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Originally Posted by Zaskar View Post

It's the rider. Seriously. The majority of cyclists will ride many bikes over many years and never experience this, while other riders will experience this on every bike they ride.
Not in my case. As I posted earlier, I've only experienced this on one bike, and I've tried everything possible to remedy the situation with no success. I've owned dozens of other bikes over the years and have never had this problem with any of them.
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Old 09-08-20, 05:40 PM
  #64  
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Originally Posted by Zaskar View Post
That's my point. As each rider with a wobble searches for the cause, they'll find a loose headset, loose spoke, hub issue, tall frame, carbon resonance issue...

Anyone who's ridden for only a couple years has ridden a bike with a loose spoke, loose headset, a wheel out of true, etc. A = B and B = C but A does not = C.
It did in my case...The bike went from skittish on descents to being rock solid once the headset was adjusted properly. This was my actual experience. Nothing you type can change that...
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Old 09-08-20, 05:55 PM
  #65  
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This is incredibly interesting to me. I knew motorcycles could get headshake in certain circumstances, but I had no idea bicycles could. With that said, I don't trust my Lynskey Backroad at more than about 37. It starts feeling, for lack of a better word, light in the the front end. Like if I pushed it, It would lose stability. I have run a lot of bikes over 40 and have bumped 50 once. I never felt anything other than perfectly planted. For those of you who have experienced it, did it feel glued to the road one second and the next it started the wobble, or did it telegraph that it was entering an unhappy zone.
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Old 09-08-20, 10:04 PM
  #66  
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Originally Posted by wphamilton View Post
Regardless of the specific cause in the given incident we know that speed wobble is a resonance with some kind of positive feedback that builds the resonance. (it could also be a negative control input feedback that is time-delayed just the wrong amount).

With it happening that frequently, I'd be changing anything on the bike that could be contributing. Sometimes (usually?) a lot of otherwise unrelated factors have to be just right to make it happen. Starting with tires even because that's the cheapest and easiest, but it would be a good excuse to upgrade the wheels. Handlebar width. Lube the headset. Weight distribution on the bike, tweaking the rider position.

If it's the case that control input is contributing, the recommendation that I've seen and which has worked for me is "stop fighting it". Also relax in the arms and upper body, but it needs to be almost instant.
Or downgrade the wheels :-) There is no reason to believe a more expensive wheel will excite the resonant frequency of the any less than a cheaper one. Id try a balanced wheel with an other weight. But then again, that may just alter the resonant frequency of the system, and push the wobble to a slightly different speed.
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Old 09-09-20, 08:37 AM
  #67  
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Old 09-09-20, 12:39 PM
  #68  
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Interesting video
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Old 09-09-20, 01:50 PM
  #69  
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Ouch! Hope you heal up quickly.

Originally Posted by JohnJ80 View Post
The classic advice given is to clamp the top tube between your knees. This works if itís the top tube (less but still effective if down tube) thatís oscillating. What this does from a frequency perspective is make your top tube shorter so that you push the resonant frequency higher. Once itís higher, then it will stop oscillating from the current input frequency because itís no longer the resonant frequency. Of course, this is going to matter what the frequency is, where you clamp your knees on the tube etc.... So thatís why it doesnít work *all* the time.

Scary problem. Been there.
J.
That was the drill for those flexible flyers of the 1980's. John gave a very good explanation of the forces involved. Basically anything that can create a vibration can cause this, so most of the suggestions may help.

I have a Peugeot CFX-10 from the early 1980s with a 61 cm top tube. It seems to wobble if anything is wrong. One item which has changed the wobble point on that bike is tire balance. Patch a tube, by the side of the road, wobble at 30 MPH. Good wheel balance, wobble at 35, so I would add wheel balance to the list of wobble causes.
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Old 09-09-20, 04:09 PM
  #70  
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Originally Posted by DangerousDanR View Post
Ouch! Hope you heal up quickly.



That was the drill for those flexible flyers of the 1980's. John gave a very good explanation of the forces involved. Basically anything that can create a vibration can cause this, so most of the suggestions may help.

I have a Peugeot CFX-10 from the early 1980s with a 61 cm top tube. It seems to wobble if anything is wrong. One item which has changed the wobble point on that bike is tire balance. Patch a tube, by the side of the road, wobble at 30 MPH. Good wheel balance, wobble at 35, so I would add wheel balance to the list of wobble causes.
Very good point about wheel balance. If the system is underdamped or resonant and that wheel imbalance hits the right frequency, it would probably set off the wobble behavior. Silca makes some wheel weights so you can actually balance that out.
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Old 09-09-20, 09:18 PM
  #71  
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Could the reason for the high speed instability is that the bike in question does not have enough trail in its fork?
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Old 09-10-20, 09:05 AM
  #72  
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Originally Posted by Racing Dan View Post
Or downgrade the wheels :-) There is no reason to believe a more expensive wheel will excite the resonant frequency of the any less than a cheaper one. Id try a balanced wheel with an other weight. But then again, that may just alter the resonant frequency of the system, and push the wobble to a slightly different speed.
Yes true, and a lot cheaper to test whether the wheels are involved if you downgrade. Just regarding upgrades, if you're like me you need a logical rationale to upgrade anything so I'm not being flippant. Those of the other persuasion, who already have great wheels, it would be a good time to get a spare wheel-set or training wheels.

We don't actually know if the wheels have anything to do with it, in a given incident. I think that speed wobble arises from incidental combinations of practically any structural or moving components and/or the rider reactions.
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Old 09-10-20, 10:06 AM
  #73  
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I believe the issue is the undampened nature of the fork that is at the root of the problem. It has been know in MCs for decades and all sorts of dampeners are available, both oem and after market. Cane creek has a dampened headset for bicycles, but it wont fit most road bikes.

https://canecreek.com/product/viscoset/
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Old 09-12-20, 08:57 AM
  #74  
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Originally Posted by jim_pridx View Post
Not in my case. As I posted earlier, I've only experienced this on one bike, and I've tried everything possible to remedy the situation with no success. I've owned dozens of other bikes over the years and have never had this problem with any of them.
But i think the question is, if you had a friend of yours try that bike, do they also have the same problem?
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Old 09-12-20, 11:21 AM
  #75  
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Originally Posted by Sy Reene View Post
But i think the question is, if you had a friend of yours try that bike, do they also have the same problem?
Of course, I wouldn't be able to answer that question with any certainty unless we actually did the test for real, but my hunch is that the bike would indeed go into a "shimmy" of sorts if another tandem team took it to a high enough speed for it to occur.
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