popeye

We had one bad (otherwise new/good tire) that would initiate a SW at a predictable speed. Death grip provides positive feedback which make it worse. I can't imagine losing it with a good chance of a high side at those speeds. That has got to be scary.

Sorg67

I do not know how I would react. At 60 years old, my body breaks easier and takes longer to recover. Therefore, I think I am going to speed limit myself to the mid to low 30 mph range. From what I have read, the risk of speed wobble is less at those speeds.

There is an out and back segment on Strava near my house. Out is down hill and back is up hill. It is not a long enough descent that I think speed wobble would be much of a risk. But, I am planning to make a new Strava segment that is only the back up hill portion. That is the most significant physical challenge portion. The out and down portion is a courage, skill and willingness to take risk challenge. The risk portion is mostly the 90 degree turn at the bottom of the steep portion of the hill. Ability and willingness to take the corner at speed is a major portion of the down challenge.

Carbonfiberboy 

Yeah and then the guy goes right back to doing wrong again. Just asking for it.

Carbonfiberboy 

I've never had a speed wobble, ever, and I've descended at 65 mph, lots and lots at 40+. Thing is, I ALWAYS descend pedals level, butt off the saddle, knees with death grip on top tube - and old style diamond frames with level top tubes, the real bummer about the new frame designs. Yes, that's a slightly tiring position, but nothing as tiring as skiing bumps. One should be able to hold that position for at least 30', no problem. When one tucks at speed, hands in the hooks, butt off the saddle and moved back, chin 2" off the stem, elbows tucked under the belly until they almost meet. At 40, that's about 1 mph slower than on my clip-ons.

If it's a fast corner, I'll drop the inside foot, but I still press on the top tube with the outside knee. I never stick a knee out at speed. I know people do it, but I prefer to touch the brake or sit up rather than go for aero drag with the knee.

The cause in controversial. Some say frame and fork design might have something to do with it. I had a slightly scary experience descending in traffic with a set of semi-aero wheels that I'd put on a Cdale 9. Turbulence from the cars would jiggle the front wheel, not a death wobble, just a little movement easily damped out, but not something I'd initiated. I never used those wheels on that bike again.

Seattle Forrest

I had a bike that seemed prone to this, about 15 years ago. No bike I've had since has done it. Not that it was a bad bike I used to have, more like the stars have to line up just right for it to happen, anybody else could ride that bike and never get the speed shimmy, like how I haven't got it on any other bike.

It only happened to me in a narrow range of speeds, like 30 to 35 mph, or whatever. So, counterintuitively, going faster can be an answer too. Only ever happened going down steep hills.

I think I remember it starting small and growing quickly. Maybe someone else can comment on this, because ever since I turned 40 I can't remember what I had for breakfast ... and it's still morning. If that's the case, stop it early.

DaveSSS 

I descend at 50-54 mph at least once a week. Never had a speed wobble in my life. I don't do anything special. I just sit on the bike and tuck down to maximize my speed.

kgcabs

Had it happen to me twice...scared the hell out of me. Was able to recover. Unweighted the saddle and knee clamped the top tube. I am 6'4" on a 61cm frame. I was cold and a bit nervous as a car was hanging back not passing. Going probably 35-40 mph. About a year ago I changed to Spinergy PBO wheels.....never repeated the wobble....very solid feeling.

colnago62

The speed wobbles I have had have all been linked to something wrong with the bike. I had a bike that was slowly cracking at the head tube. I also had a bike that had a slightly lose headset.

diphthong

having had speed wobbles multiple times, always descend significant grades with one knee against the crossbar at all times and a relaxed grip because i'm expecting wobbles.
have still had a few despite instituting these measures with both a weighted and unweighted saddle. if you haven't experienced, you don't want to.

Rides4Beer

Thankfully I've never experienced it, looks terrifying. I've done multiple 80+kph descents on three different bikes with no issues. I descend seated, in the drops, pedals level, knees tucked towards the top tube but not touching it.

Chuckles1

That is a scary story. I've never experienced it, but would be very leery of taking that bike up over 40mph unless I could determine the cause. Good luck.

MinnMan

Totally don't want to. But reading this stuff is the start of a survival defense if needed.

I'm not sure I'm getting all of the pointers though. The relaxed grip makes sense if you are coolheaded enough to pull it off, but would seem even harder if you unweight the saddle?

BoraxKid

This passage is especially interesting to me:

https://cyclingtips.com/2020/07/bicy...-to-stop-them/

So it seems that this issue of speed wobble is much more likely to happen on those older, vintage steel frames that certain people gush over, and it's much, much, less likely (though still possible) to happen on a newer, carbon-fiber frame (aka "plastic bikes" as the retrogrouches like to say). I wonder if we'll ever see a manufacturer posting a warning label on a frame to indicate its Hopf bifurcation predicted speed at which wobble becomes a safety concern. Maybe the marketing departments can start touting how fast their company's bikes can go before they start to wobble? Or would people take that as a challenge? Interesting topic, indeed!

JohnJ80

Not sure I agree with that. It’s a classical mechanical resonance or under damped issue where some repetitive frequency at the right frequency sets up the wobble. Depending on what’s wobbling - top tube, fork, chain stay etc... you need to damp that member. That’s why often clamping the top tube with your knees stops the wobbling because you’re changing the frequency that that member resonants at which happens to be related to the speed you’re traveling (or, more accurately, to the wavelength of the frequency). That’s also why speeding up/slowing down can help or moving your weight placement. The problem with braking is that it can increase the amplitude of the oscillations until you slow down enough to get out of the resonant/under damped frequency range. The problem with speeding up is that you eventually need to pass through that slower resonant frequency range at some point. So it’s a tricky problem and needs to be solved because if you hit it just right the amplitude of the oscillation can increase rapidly to the point of it being uncontrollable. “Uncontrollable” means to the point it’s not possible to control regardless of your bike handling skills.

So one does need to try and find the cause of the wobbling. All the advice on checking hubs, head sets, etc... are valid. And often the solutions are counterintuitive because they are frequency/wavelength related more than anything else.

That said, it’s possible to create a frame out of pretty much any material that hits resonance. I have a stainless steel frame that I’ve never seen it wobble. I used it for light touring because my other bike wasn’t available at the time, with a light load of less than 20lbs extra on the frame, I would get a pretty severe wobble at around 14-15mph. Took the weight off and it was fine and has never been an issue since. That’s why any frame can wobble under the right conditions.

BoraxKid

I don't understand your logic here. The article I cited explicitly states that speed wobble is more likely to occur on road bike frames from the 1970s &1980s due to their resonant frequencies. It then goes on to say that manufacturers today are designing frames that have a resonant frequency that requires much higher speed to cause a wobble. So while it is possible to experience speed wobble on today's carbon bike frames, their designers have accounted for it and made it much less likely to occur.

Seattle Forrest

There are several things you can do if you get into a speed wobble, but you can do any one of them, you don't have to do them all. Get your ass in the air and your grip on the bars won't matter.

When it happens, you don't think "oh this is that thing we talked about in the road forum" it's more like the bike moves and everyone's immediate reaction is to reflexively try to correct.

Seattle Forrest

Probably not because it'll be different for each rider. The more you weigh the harder it is to get this to happen.

BoraxKid

That's a fair point. But we do already see aero gear advertised with a lot of qualifiers when stating time savings claims. Maybe the bike manufacturers could do that? "Guaranteed no wobble up 75 mph for a 150 lbs rider!" Seems like decent copy, but I'm not one of those "mad men" you know?

JohnJ80

correct. I don’t agree.

the range of uses is so wide, the variance of users also so wide, the virtually infinite variation of road surfaces and conditions are impossible for a manufacturer to accommodate and guarantee that the frame won’t be under damped or resonant In some set of conditions. I think it’s possible to get any frame into a condition in which can do this depending on how it’s loaded and ridden. And, in fact, that has been my experience.

jim_pridx

This "large bike frame" idea has me curious about a tandem that my wife and I own. I'm 6'3 and typically ride a 61cm frame as well, but the tandem I'm speaking of seems to want to go into a "shimmy" mode at about 42+ mph while going downhill. Of our three tandems as well as all of my solo bikes, this is the only bike that I've experienced this problem with. It's happened with two or three different wheelsets, too, so it must have something to do with the fork or the larger frame size up front. Fortunately I've been able to get a grip on it before going into a full "wobble" - so no crashes - but it's a frightening experience, to say the least. Needless to say, I'll never take us above 38 to 40mph on that bike ever again.

Racing Dan

This video contains some interesting insights even if its from a MC point of view.

blakcloud

Wow good stuff here, thanks for posting this. In my case the more I braked, the harder the bike was to handle. It just kept getting worse until I crashed. At the time of the incident I just wanted to stop the bike so I could re-group, that was my focus.

Two factors that may have influenced what happened to me was the downhill went around a corner and I went straight into a head wind which was about 20-30 km/h and the second was just before the wobble I hit some really rough pavement which may have unsettled the bike. One of the problems with trying to overcome the possibility of the next speed wobble is my inability to control the dynamic risk factors. There will always be the static risk because the bike is the bike.

znomit

I used to get wobbles frequently on my Trek 1.7c. It was set up with a small handlebar bag and a heavy Maxis refuse front tyre. Downhill with a strong crosswind would cause them. Quite scary but the top tube trick worked really well once I got my wits together. I think they went away when I changed tyres. OP you might want to try swapping out tyres.

JohnJ80

I’m an electrical engineer with a background in control system and semiconductor, but the concepts in a mechanical system are the same (and so is the math). Basically, any time you have an underdamped system and you hit that system with an impulse at the right (i.e. resonant) frequency you are going to get oscillation that (probably) decays over time. When the wobble gets persistent it means that either the frequency you are hitting the system with is persisting (i.e. washboard road) or the bike is highly susceptible to that frequency. You change that by damping the frequency/oscillation, by changing the “length” (from a wavelength perspective) of tubes or changing the mass of the vibrating thing. It’s obviously a lot more complex than that with something like a bike, but it still offers clues about what to do.

First off, I’d make sure that your headset is tight, your hubs are properly adjusted and you brake rotors are tight to spec. I’d also make sure your rotors are clean and have no tendency to squeal - all of these could amplify the effects of an frequency input at the right frequency or produce the frequency themselves (i.e. brake rotors).

If it still persists, I’d change to a wider tire and I’d lower the tire inflation to get a more plush ride. That is going to damp any frequency input from the road (you mentioned rough road). I’d also be extremely careful about hitting big road defects like pot holes since those are an impulse that is compromised of many frequencies to get the sharp edge hit you feel. So even though it’s not a continuing frequency input like the washboard road might be, it can have sufficient energy in the frequency that sets your bike off. The wider tires/plusher ride will help here too. Silca has a great tire inflation calculator which will help. Most riders have their tire pressure too high anyhow. If that’s you, then this could be an easy fix.

If it happens a lot when braking, then I’d look at the rotors. If your rotors are getting worn they can get thinner and set up an oscillation. Resonant frequencies are one of the big worries in designing braking system so I’d even look at changing to a different rotor - one that is thicker and stiffer would be a good place to start. May not look as cool or be as light but it’s going to behave differently in terms of oscillation.

If it’s the wind, then I’d be looking at things that the wind might have an effect on and could start vibrating such as handlebars. I suppose certain aero shaped bars could be a problem. You should be able to debug this by changing hand position on the bars. I’d look at putting my hands on the half of the bar that’s nearest the stem and try moving them in and out and see if that stops it. If it doesn’t, then it’s not the bars.

The classic advice given is to clamp the top tube between your knees. This works if it’s the top tube (less but still effective if down tube) that’s oscillating. What this does from a frequency perspective is make your top tube shorter so that you push the resonant frequency higher. Once it’s higher, then it will stop oscillating from the current input frequency because it’s 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 that’s why it doesn’t work *all* the time.

Scary problem. Been there.

Perfect example. Adding mass in the wrong place and changing the spring constant in the tire are two places that could lead to underdamping. That tire is probably stiffer with less damping of the road vibration, and that handlebar bag depending on how it’s attached and where it’s attached is helping to set up an oscillation in the front end but probably in the bars. Stiffer bars might help that.

I agree with the idea of changing tires but make sure you reduce pressure so you have a cushier ride. Generally faster on the road that way anyhow.

J.

Hapsmo911

I would check the stem alignment and as someone else stated, check the headset compression.