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Re: Speed wobble on your carbon bike [sebo2000] [ In reply to ]
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That's interesting, I hadn't heard that before. Any link you might of read and can share where that is discussed with data?
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Re: Speed wobble on your carbon bike [sebo2000] [ In reply to ]
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sebo2000 wrote:
Ai_1 wrote:
Did you do anything to try and stop it? Braking, bracing the top tube with your knee, etc....?


Wobble was very common on all the bikes with the same size of headset bearings, that means almost all the old bikes are experiencing it, old Cervelo S5 were notorious.

It was fixed on all the new bikes by having 2 different size headset bearings, the bigger the difference in size the less chance of getting the speed wobble.

To stop the wobble, simply stand on the pedals, quick stand off the saddle stops it instantaneously.
Seems to me that raising off the saddle would have a similar effect to bracing the top tube but for a different reason. i.e. bracing the top tube adds a contact point, standing removes one but wither way you change the feedback mechanism. However that doesn't quite match the suggestion that the head tube bearings are responsible. Plus I've come across mild incidents on my Canyon Ultimate which has very different top and bottom bearing sizes. Bearings may be one source of the initial perturbation but are we sure it's a necessary element of the behaviour?
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Re: Speed wobble on your carbon bike [lanierb] [ In reply to ]
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2015 Trek SC 7
Aeolus 7 wheels
Full IM compliment
training ride for IMLou, was practicing "bombing" down hills to prepare for rolling hills (to carry as much momentum back up)
Happened twice going down long descents, hitting ~37-40 mph. when moving from aero to basebars to prepare for braking 1/3rd way down (this particular hill had a sharp curve at bottom.)

Took it to local Trek shop. they took apart the stem and found both stem bolts were a bit loose.
Mechanic checked everything else (said I probably should replace steering tube bearings, which were still the original ones, agreed with that)

Tested again and no more speed wobble.
Last edited by: srschick: Sep 27, 17 9:37
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Re: Speed wobble on your carbon bike [Slowman] [ In reply to ]
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The bike was a generic Chinese TT frame size 54, 50mm slammed stem with Profile T2 aerobar.

Wobble occurred on a moderate downhill at around 28 mph. The ride was a loop so every time I passed that downhill, same wobbling occured.

The frame size, stem, etc...were irrelevant bec according to my mechanic, cause of the problem was the entire front end (headtube, spacers, stem etc..) was not pressed properly to the fork!!!!!. I remembered that I removed one spacer the day before and did a terrible job of putting the front end back to the fork.
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Re: Speed wobble on your carbon bike [joesullivan66] [ In reply to ]
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joesullivan66 wrote:
Did you use any particular technique to stop these wobbles whilst they were happening? I have read getting up out of the seat, and also putting your knee against the frame are good ways to stop it, but as you have had it happen three times it would be good to hear if you had any tips?

Nothing in particular that hasn't already been mentioned here and elsewhere re: stopping wobbles. It's a bit like hiccups - there are lots of ways to get rid of them, but they all boil down to changing your breathing (e.g. holding your breath) so that you disrupt the diaphragm spasms that cause the hiccups. Similarly, when you get a wobble, you have to change something in the bike/rider system - it's often effective to grip the top tube with your knees/thighs because that often serves as a damper, absorbs some of the wobble's resonance, and does enough to disrupt and stop the wobble.

There are may be other ways of stopping a speed wobble - standing up, pedaling faster, shifting position - but it can be hard to do those when in the grips of a true speed wobble. The nice thing about the "grip the top tube" technique is that it tends to secure you to your bike.

Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099
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Re: Speed wobble on your carbon bike [refthimos] [ In reply to ]
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refthimos wrote:


This one happens at 0:41:
https://vimeo.com/42816611



That looks absolutely terrifying! Makes me glad I'm a flatlander. And makes me wonder how I survived the descent from Loveland Pass on my junker 90's era mountain bike on beach cruiser tires when I was on vacation there last year.

"They're made of latex, not nitroglycerin"
Last edited by: gary p: Sep 28, 17 17:29
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Re: Speed wobble on your carbon bike [Slowman] [ In reply to ]
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Happened to me yesterday.
New Cannondale System six, size 60, 120 mm stem and two small spacers under it. I just filled both bottles and proceeded down a straight shot descent. The wobble hit at about 45 mph and was incredibly scary. I was resigned to the fact I was gonna eat pavement but I slowed it down gradually. It took forever to stop and took everything I had to control the bike. It was windy and there was passing traffic, might have been the perfect storm of conditions to induce it. I hope so because I love the bike and have only had it happen once years ago on an old litespeed vortex with old zipp 404s. I sold that bike not long after.
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Re: Speed wobble on your carbon bike [ridenfish39] [ In reply to ]
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Nice save.

I’m convinced mine happened because I didn’t clamp down tight enough on my zip aero skewer. Two or three different occasions. Hasn’t happened since I’ve gone back to my stock Reynolds skewer.

But similar conditions for the first and second wobble. Fast decent strong crosswinds. Third wobble made no sense to me as it was neither fast nor windy. Which is why I checked the skewer.
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Re: Speed wobble on your carbon bike [SBRinSD] [ In reply to ]
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FWIW I had issues on a Crockett after reassembling it from an overseas trip.

I had forgotten an upper steerer cinch ring that works with the bearing. This would cause the steerer to almost imperceptibly move around. I could imagine on some bikes you'd never see it.

It wouldn't get bad until over certain speeds.

If the steerer doesn't stay within the plane of the bearings, it's trouble.
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Re: Speed wobble on your carbon bike [ridenfish39] [ In reply to ]
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With modern carbon bikes it doesn’t happen near as often. The flex in steel bikes made them a natural candidate for wobble. Larger frame sizes in particular are vulnerable since most manufacturers do not engineer each size to account for the various fit and handling characteristics - speed wobble, fit or otherwise.

Life is too short today to own a bike that is vulnerable to wobble on fast descents. Certainly for me anyway, since I still ride in the mountains quite a bit. I can barrel down a mountain at 50+ eating lunch on my Spec Tarmac and it is just stable as a rock. I am on a 58 though, so it’s not their largest frame. And I run D/A wheels, which are not flimsy.

The System Six should be a good bike, but it is a 60. I would try a different set of wheels, double check headset tightness, and if no luck then just move on to another bike. Having to change your descending position or clamp the top tube with your knees is just stupid. Don’t compromise your riding skills, get a bike that doesn’t wobble. I suspect most newer carbon bikes don’t. I can virtually assure you a 58 Tarmac doesn’t.
Last edited by: NealH: Nov 26, 18 7:17
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Re: Speed wobble on your carbon bike [NealH] [ In reply to ]
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I'm really not convinced.
You're putting everything down to the bike like it's established fact. How can you be sure?
I go down smooth roads in predictable conditions at 80km/h perfectly happily. However, I have had a couple of instances of speed wobbles on rigid bikes (of very average size) when descending at speed and having disturbance to the bike (I'm sure road surface initiated one, probably both).
I think the primary cause is more likely rider induced oscillation due to coupling of control input and resulting bike motion.
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Re: Speed wobble on your carbon bike [NealH] [ In reply to ]
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It’s crazy. I fly down hills at 50 plus on my Ridley and Synapse and don’t think twice about it. I’ll check the headset when I get home. I know for a face the thru axles were both tight
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Re: Speed wobble on your carbon bike [ridenfish39] [ In reply to ]
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ridenfish39 wrote:
...The wobble hit at about 45 mph and was incredibly scary. ...


Hi ridenfish39,

Sorry you had that experience.

Wobble is related to system stiffness, so bigger bikes are (all else equal) more susceptible. We've engineered increased stiffness with increasing sizes so the bigger frames are stiffer in a proportional response, but any structure still has a natural frequency so can resonate under the right (wrong?) conditions. Even in the medium size, the SystemSix is stiffer than last generation aero bikes so is less susceptible to wobbles, and the larger sizes only get stiffer, but that said, the higher stiffness just raises the natural frequency so that if/when a wobble starts, you're going at a higher speed!

In the old days nearly everyone's bike would wobble, so we all knew what to do: "touch your knees to the top tube, or stand up and unweight the saddle a bit."

This good advice is from a thread you might find helpful: https://forum.slowtwitch.com/...ost=5103061#p5103061

More background that helped me understand shimmy or speed wobble by Jobst Brandt, still true today: https://www.sheldonbrown.com/brandt/shimmy.html

Cheers,
Damon

Edited to add: While I was typing several folks also posted.
1. The idea to ditch the bike works *if you're sure your new bike is stiffer.* We've measured and the SystemSix and it's among the stiffest, so in your case, changing is unlikely to help. In neal's case, the Tarmac of a generation or two ago was among the stiffer bikes (according to data measured by TOUR Magazine), so that may help explain his success at avoiding speed wobble.
2. Sure, check skewers (or through axles) or headset or wheels, but unless they affect stiffness they are unlikely to help. Because wobble requires a combination of conditions, by chance some riders have appeared to solve wobble by adjusting things, but the natural frequency only depends on mass and stiffness so it's unlikely the various mechanical things people have checked really have changed anything.
-DGR

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
Last edited by: damon_rinard: Nov 26, 18 7:33
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Re: Speed wobble on your carbon bike [damon_rinard] [ In reply to ]
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I recently played an episode of the Velonews podcast and they had a bike maker on there who described exactly this kind of resonance in a frame at certain speeds...I'm pretty sure it was this one.

https://www.velonews.com/...-lennard-zinn_480109

even if it doesn't answer your question it was still very interesting..

HTH
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Re: Speed wobble on your carbon bike [damon_rinard] [ In reply to ]
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Damon, the System six is the stiffest bike I’ve owned. And I’ve had a bunch including the original system six, one of my favorite bikes ever. I’m hoping it was just the perfect storm of crosswind and traffic passing by. I am on a 60 cm with the 120 stem and only 2 small spacers underneath. I may have been just too relaxed as I was on the hoods just cruising down. I’ve done that hill plenty of times on my other bikes but this bike is definitely a bit of a handful in the wind.
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Re: Speed wobble on your carbon bike [ridenfish39] [ In reply to ]
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ridenfish39 wrote:
Damon, the System six is the stiffest bike I’ve owned. And I’ve had a bunch including the original system six, one of my favorite bikes ever. I’m hoping it was just the perfect storm of crosswind and traffic passing by. I am on a 60 cm with the 120 stem and only 2 small spacers underneath. I may have been just too relaxed as I was on the hoods just cruising down. I’ve done that hill plenty of times on my other bikes but this bike is definitely a bit of a handful in the wind.

Hi ridenfish39,

Sounds like you understand it pretty well. It seems likely it was the perfect storm (good way to phrase it!).

Relaxed is less likely to wobble; human reaction is about the same frequency and is almost never in phase with a wobble so could actually make it worse (but even though I know that, I still can never loosen my grip once it starts! Just clamp the top tube...).

The deep rims definitely have more sideforce than shallower, which matches your experience. And passing cars changes the steering torque, so yes, you have to stay in control with deeper rims, especially in unsteady conditions. That said, we've measured steering torque in the wind tunnel and the response of the Knot 64 wheels is more gradual (less unstable) than other similar depth wheels, across suddenly varying yaw angles, which is what you get with a crosswind and passing cars.

Maybe give it a try, on your next downhill try to start the wobble and try to clamp the top tube. Tame the wobble! Make friends with the wobble! Master the wobble! Okay, just kidding, but a practiced response, if it ever happens again, can come in handy.

Or just memorize: clamp the top tube!

Cheers,
Damon

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)
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Re: Speed wobble on your carbon bike [Slowman] [ In reply to ]
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Been road riding for 30 years on at least 15 different bikes. I have a Raleigh Militis carbon frame that has a bad speed wobble. It is a really nice carbon frame with an aero down tube that weighs 880 grams.

At about 40-42 mph, the front end starts shaking violently. I have experienced this on about 4 different road descents, over multiple rides and years. I regularly ride mountains that gain or lose 1000-1500 vertical. It has a 120 mm stem, sized 55cm bike, stem slammed. I have even "played" with it trying to see if clamping my knees to the top tube or braking (which makes it worse) stop it.

What has mattered a lot is wheel choice. Ksyrium SL wheels: has speed shake, Campy Zonda wheels: none, Hed Jet 6+ - speed shake at 35 MPH awful. I think the fork / front wheel choice is the main issue, the commonality of the Ksyrium SL and the Hed is that they are both big wind dams in the front end.

I am just going to sell it. I have an older titanium / carbon Serotta that is a downhill carving machine, feels steady as a rock and you can rip down any descent at warp speeds.
Last edited by: endosch2: Nov 26, 18 8:23
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Re: Speed wobble on your carbon bike [endosch2] [ In reply to ]
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eek. Never heard of this. Another reason I limit myself to 35mph on the downhills..... Whatever, I want to live, I will try harder on the climbs.
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Re: Speed wobble on your carbon bike [triczyk] [ In reply to ]
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I live for downhill speed. Fastest I’ve gone is 62 according to my garmin. I will honestly be nervous next time I bomb the local hills on this bike. There are a few where if you just tuck and coast you’ll hit 50.
I think I might look for an extra front wheel in a 40 mm depth. Never had an issue with my Noah and it has a 45
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Re: Speed wobble on your carbon bike [Slowman] [ In reply to ]
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1. moots rsl 60cm (slightly too small for me)
2. 3t funda fork
3. going 45+mph

Loved that bike besides the wobble. Counterintuitively, getting your butt off the saddle and losoening grip will mitigate/end a speed wobble.
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Re: Speed wobble on your carbon bike [ridenfish39] [ In reply to ]
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Try different things, but my guess is that you will not be able to eliminate it. And I don't see how one can enjoy mountain riding knowing, that they don't know, what will happen on the next descent. There will always be that grain of fear at hand - that the bike might start the death wobble. Staying so attentive to it will likely have the rider slowing down or not putting full attention to the descent and enjoying it. While I respect Cannondale and wish them the best, I would not keep a bike that I could not be comfortable with. The comment made by Ramon to just clamp the top tube is totally unacceptable.

The System Six that you appears to be a relatively new aero bike. The newness concerns me, as I wonder just what testing they have done. Wait till more feedback makes it way across the net, and you might find that you are not the only one experiencing this. Cannondale should take this feedback and immediately get it resolved (much like Calfee did a number of years ago), whether the culprit is their frameset of some third party component issue. Stepping to the sidelines, and saying to clamp the top tube is enough for me to eliminate consideration of a System Six in the future, maybe other models too. However, if the bike was going to only see flatter terrain, it probably wouldn't bother me....probably.
Last edited by: NealH: Nov 26, 18 17:00
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Re: Speed wobble on your carbon bike [NealH] [ In reply to ]
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The shop owner has one in a 58 cm and has done well over 50 mph on it with no speed wobble. Set up similar to mine with 2 spacers and a 120 mm stem. I will be really attentive next time I push past 45 mph, if it happens again I will (depressingly) have to sell it
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