1.) 56 cm Cannondale Evo.
2.) Zipp SL70 w/ 110mm -17 stem. Slammed.
3.) Drafting huge truck at >40mph for fun, coming out of the draft things got dicey for some reason.

Had been a while since I'd gotten a speed wobble; had almost forgotten how nasty it could be.

1. Giant Trinity composite Lg
2. Giant brand Aero pad set up, many spacers under the stem (8cm maybe), Zipp vuka bull base bar (this has since been remedied).
3. Descent on the LPlacid course, think my flexy Carbon wheels (old style Boyd) flexed on rough pavement, nicked frame, and then bike got all squirrelly with speed wobbles...going 40+mph

to me, when i say or hear speed wobble, it's not a 1-time thing with a bike. it's a particular characteristic of that bike, that bike's parts, maybe that bike's rider. it's just like a shimmy in your car, where it might start at a certain speed and then stop at a higher speed. at a particular point, the bike starts to oscillate, just like the wheels in your car during a front-end shimmy. it's very unnerving.

sometimes it happens in a freak situation, on a long descent, you're cold, you get "sewing-machine leg," and that is the agent that starts the wobble. but usually you don't get it once only.

is this what you experienced? or was it a very disconcerting buffeting from the truck once you left the draft?

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Dan Empfield
aka Slowman

You flew through his jet stream? Hasn't Goose's death taught you anything?

1) Cervelo P5-6 54cm
2) P5-6 config with 10mm spacer and the low profile setup.
3) Slight down hill at 41mph. Roads were fine. Not wet or ice. No wind.

I suspect my 2008 Zipp 404's though. They have seen their better days. The tires are GP 4000s. Front is fine, no major flaws, rear has a slight flat spot on it from the trainer.

Not the first time getting speed wobble with these 404's and on different bikes. Looking forward to new Flo 60/90.

I'm familiar with what you meant by speed wobbles. Used to call them "death wobbles" on skateboards that were the same sort of thing and I used to get a particular speed wobble on an older bike down a steep descent with some consistency.

Something about the speed I was at combined with the airflow coming out of the draft (and possibly my position at the time?) made the bike go into that same classic speed wobble, where it was starting to oscillate and had the feel it was about to go out of control. It lasted significantly longer (or at least felt like it did) than just the initial wake of leaving the truck. Tried de-weighting the saddle and that seemed to correct things enough that I slowed and kept it under control.

Reminded me a little of the video I've seen where the wobble could be induced by banging the handle bars. Perhaps coming out of the draft was a little like that.

was it the only time you experienced it with this bike? when did it stop? only when you slowed down?

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Dan Empfield
aka Slowman

Ha, nice! Like Mav, I have a need for speed even if it sometimes isn't the smartest thing in the world. So fun right up until I thought I was going to die.

So far the only time, I don't think I usually get up to that speed on this bike, so not sure if it is the characteristic frequency of this bike to have issues at that speed yet and I'm not excited to do more experiments along those lines. It stopped as I stood up a bit off the saddle and slowed down. Pretty sure it was still happening well after the major wake of the truck was gone, so I think the truck wake initiated it and wasn't what was keeping it going.

Also, check the wheel dish. Especially, 11 speed rear-wheel dish.

Cheers,

G

Based on my experience, I think there's at least one more bit of information you might want to ask for...

1. 2011 Madone 6.2, 58cm H1 geometry
2. 110mm x -7deg Bontrager RXXXL stem, 42cm Syntace carbon bars, 15mm of spacers
3. transitioning from hoods to tops near the stem (aero tuck for a descent)
4. what else was on my bike: a chunk of steel equivalent to a fully loaded 2-pack (e.g. equivalent mass of a pair of full 28oz bottles and all the stuff triathletes would probably carry in the storage compartment), cantilevered out behind the saddle as part of ride evaluation of the 2-pack attachment hardware

#4 is important. The bike went into speed wobble almost instantly when I removed one of my hands from the hoods early in the descent. The same bike, sans the simulator, has never speed wobbled with or without hand movement in any other condition at speeds in excess of 55mph.

So of course I went out and experimented some more a couple weeks later. Same load (preproduction prototype 2-pack this time, fully loaded) installed on 2014 9srs and 7srs SCs with multiple wheelset combinations (including Aeolus D3 9's, old Aeolus 5.0, old RXXXL tubie, Aeolus disk rear, H3 tubie front, etc) and I experienced zero speed wobble at speeds approaching 50mph with random crosswind gusts in the range of 10-15mph. Ran same course, same day, at same speed(s) with the aforementioned Madone on a pair of A9's with and without 2-pack and once again got near instant wobble when it was on and rock solid when it was off.

Yeah, sometimes I'm a guinea pig. I love my job.

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Carl Matson

sounds like an experience in extreme turbulence rather than speed wobble caused by exciting the natural frequency of the bike frame.

Only ever happened to me when I was about 9 on my Raleigh Mini Burner. When my sister found me on the road she thought I was dead..!

But, reason for posting is this is a great opportunity to share a youtube video posted by a certain "drinard" ...
https://www.youtube.com/watch?v=xODNzyUbIHo

Didn't think about the single bottle off the back of my saddle. Maybe it was the position and weight of the bottle for me. It was sitting rather far back, hard for me to reach.

Are we talking a normal slight wiggle... or a full on severe head shake? Under braking? Mid-corner bumps? crosswinds? aerobars? sitting up? How upright. Sometimes have less weight on the front and make it much worse I think.

I've had some shakes, but overall consider them normal and expected in certain conditions.

I've even had loose headset bearing and loose front and real wheel bearing and never noticed anything unusual. I'm also very relaxed on the bars at high speeds. That's the key. You should always "guide" the bike, and use counter steering and pedal weighting, never, ever "steer" anything with 2 wheels above about 5-8mph.

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TrainingBible Coaching
http://www.trainingbible.com

Felt DA4 56
2nd shortest little stubby stem cocked up about 45 deg angle
downhill ~40mph - in aerobars. Pretty sure it was the worn out front tire - pulled from back, so squared off pretty well. Never happened again once I got new tires.

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Proud member of FISHTWITCH: doing a bit more than fish exercise now.

1) Canyon Aeroad 2013 Model - Size XL
2) Stem 100mm, Handlebarwidth 44mm, 1cm spacer.
3) Heading down Ou Kaapse Weg in Muizenberg, with speeds of 82km/h. Was not supermooth tarmac. Just suddenly felt like my front part of the bike started to wobble, and thought I had a flat. Initial reaction was to brake slowly, as I could not look down properly, and it was my first ever speed wooble. Felt like the bike was going to collapse under me, a horrendous feeling. Finally got slow enough to, and my next reaction was to unclip so that I could have my legs out for balance. Felt like the right thing to do. Did notice that if I Pressed the brakes to hard, that the wobble got worse. Eventually rolled to a complete stop, and felt like throwing up. Ever since then I have struggled to do high speed descents again, which probably comes down to a mental issue. And did sell the bike a month after, as I did not trust it anymore.

Cyclist who was behind me said he thought I was going to a a complete wipeout, and he saw steam coming off my wheels at the back, which was probably from me breaking, and the road being a little damp in the morning, although it was like 25degrees celcius.

Have worked my way through three roadbikes (Parlee Z5SLI, Trek 4.3) since then, and only now I have finally found a bike a C60 that I trust for a fast descend!

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My Blog - My Tweets - My Strava
My Bikes - CF SLX, 622SLX, O-1.0, AL9.0, 4.3Disc, Slice BI, C60

interesting. tell me what you think about mass above the ground, distant from the center of mass, and its contribution to speed wobble.

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Dan Empfield
aka Slowman

PS where I work we have a 1200+ ft broadcast tower, which is a replacement for the mast that went before it which was about the same height. It was a cylindrical structure supported by stay wires under high tension. It had been standing for decades. The structure, stay wires and anchors were inspected and oiled regularly and meticulously. And then one day it fell over. The analysis showed that a very specific and sustained wind speed from a particular direction could cause oscillations of a particular frequency, which in turn could cause a standing wave to be set up on one of the stay wires, if the wavelength of the oscillation had a particular relationship with the length of the cable. And when it finally went ping and detached itself the whole bloody thing was pulled over by the tension of the other wires. And Yorkshire didn't have any TV for a long time...!

A cable is a simple object and when considering its length you are talking about nice and simple limited degrees of freedom. Any object can have a natural frequency that it likes to vibrate at, and multiple resonant frequencies when you consider all of the degrees of freedom and then the harmonics. When you consider the structures and sub structures that make up a bike, who bloody knows what conditions could make a bike go wobbly!

Good luck!

I think I don't know too much more than what I experienced. Moreover, I'm not a dynamics guy, so I'm sure what follows will imperfectly sketch out my theory. (paging epic-O!) I theorize that cantilevering a bunch of mass off of a "corner" of this system of (damped) springs that is a bicycle and rider has a higher probability to excite the springs than if it were contained in, say, the main triangle. The further you are from the fixed or contact points, the more bounce...like a diving board. That I was fine until I removed my hand(s) from the bar, and that by doing so I was briefly but significantly changing the system stiffness & damping, seem to mesh with the conventional wisdom on what induces and reduces (once initiated) speed wobble.

Came across this somewhat similar (conceptually anyway) scenario on a recumbent forum.

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Carl Matson

I know exactly what you are asking. (Google Jeep Wrangler death wobble. Oy!) I've never experienced it on a bike. Sideways forces due to crosswind with deep carbon wheels sure. We know what that is and how to deal with it.

1) Cervelo 2010 P2, 56cm
2) 110 stem, slammed, Vision bars, Zipp 404 tubulars
3) Hill decent during a race, started at about 35 mph.

I added counter weights to off set the valve extender weight on my Zipps and never experienced the wobble again.

Never had a speed wobble in 25 years of riding Carbon bikes (first carbon bike was a Kestrel 4000). I have had speed wobbles on Columbus SLX tubed steel bikes at ~ 70-80 kph (in cross winds), but nothing that changing the harmonic by taking my two knees and clamping them together to the top tube did not resolve....just changed the fundamental harmonic frequency of the bike by doing that.

Great Timing...

2014 Speed Concept. Rear bottle setup. Somehow my fit got really screwed up and I was extremely too far forward on the bike from the saddle to my aero bars. I experienced a severe speed wobble every time I went down hill and in excess of 30 mph with my hand position being in the bull horns. It happened 6 times in two days of riding. Needless to say I scheduled a new fit immediately and they moved my saddle back and got a mid-far stem to replace the low-far stem. So far the speed wobble has disappeared but those two days of riding were pretty scary.

ETA. I wasn't really sure what had happened (this was a pre-Tahoe, 2013 course recon ride) so I rode back up to the top and tried it again and the exact same thing happened. This makes me believe in the oscillation/harmonics of the bike theory at a certain speed. I was very glad to experience this before race day. On race day I preemptively put my knee against the frame on the descent and despite hitting similar speeds I never felt the bike get wobbly.

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----------------------------
Jason
None of the secrets of success will work unless you do.

2008 Felt DA, 54 cm
Short stem, flat
HED vantage 8 aeorbars, bottle between the extensions
zipp 808 FC CC with a disc cover on the rear

around 40 mph coming down Brockway in IM Tahoe

If I stayed off the front brakes, and kept the speed below 45 I seemed to be ok.

No bottle behind the saddle, just a small repair kit under the seat.

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Ryan

1. 2012 Specialized Shiv Comp Rival -- XL
2. Stock alloy bars sitting on one inch of spacers between the bars and head tube; Flo 60 front wheel with Continental Attack tire.
3. I was descending from Spooner Lake during America's Most Beautiful Ride in 2013. I was going 40+ in my aerobars and almost lost control of my bike. It felt like a cross wind gust caused my front wheel to lose contact with the ground and I'm still not sure how I managed to get back into control.

I have also had the pleasure of dealing with bike shimmy or wobble at high speed. The physics is very interesting. Many mistakenly attribute the phenomenon to resonance frequency but that is not correct. It is actually due to the Hopf Bifurcation. Apparently all bikes experience the Hopf bifurcation at a particular speed. For most bikes and riders the speed is much higher than they ever attain so they never experience it. The classic Tacoma Narrows bridge collapse which we were taught as an example of resonance frequency was also an example of Hopf Bifurcation. There is a very detailed explanation under Lenn Zinn's column at VeloNews. Just search on Hopf bifurcation to see a couple of threads. Also some cool video as I recall. Carl's experience with the rear weight is rather an interesting story. I suspect the weight impacted the torsional stiffness of the frame leading to wobble at speed. Generally the bifurcation from a stable to an unstable front end will occur at a particular speed. Get above that speed, usually on a downhill, and away she goes!
Joe

Great videos and article. Very Interesting Thank You.

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Dan Kennison

facebook: @triPremierBike
http://www.PremierBike.com
http://www.PositionOneSports.com

Only once in about 10 years of riding.

1. 2012 Orbea Ordu size 54
2. Stem maybe 110, 2 spacers, Profile cobra wing(?) with s-bends
3. Riding in Tuscon at Sanguro. Had just started the descent heading back into town from one of the overlooks. Happened within 50m. Shot me hard left into the other lane. My only thought was go down before you hit a catcus. I ended up having a rear blowout prior to coming to an abrupt stop in the sand.

Not a new bike, but my Ocotillo59DE twice going down Donner. This is why you will kill me in the race, I will be braking for dear life trying to make sure I make it down that hill alive.
Have only seen at high speed so I just try to stay under 30 MPH.

.

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Dave Campbell | Facebook | @DaveECampbell | h2ofun@h2ofun.net

Boom Nutrition code 19F4Y3 $5 off 24 pack box | Bionic Runner | PowerCranks | Velotron | Spruzzamist

Lions don't lose sleep worrying about the sheep

1st:-

Scott CR1
110mm stem
10mm spacers
Kysirium elite whels
Ritchey headset
23mm michelin pro 2 clinchers

Downhill corse chip seal with intermitent rougher patches..
Hit rough patch at 55kmh approx, tightened at the controls and the bike erupted into a voilet speed wobble..
Unable to steer effectively, rad bears left, i moved toward center of lane before gaining control.
Oncoming vehicle and myself very glad i missed them..

Total strip and rebuild revealed a slightly worn headset bearing and a very mild 0.8mm, bucle in front wheel..

Root cause was my reaction to the bump ie I CAUSED THE SPEED WOBBLE BY CLAMPING UP AND REMAINING SO AFTER IT INITIATED.

This happened to a far lesser degree 2 more times before I changed out the headset ie adjustment didn't lessen the propensity.

In short the conditions and biek can initiate it, the escalation is the result of the rider..

Second time;

LOOK 695
HED stinger 4
110mm stem
10mm spacer
Again downhill, at 87kmh.. passing through a ravine the hillside shading the road on one side ceased creating a funnel of wind...
This caught the bike side on severely causing a swerve, and almost simultaneously a rough section of tarmac.... the correction by myself and again tightening up caused a very severe speed wobble until it was slowed to 40kmh... then it ceased.... no oncoming taffic, but the cyclists i was passing about crapped them selves when they saw what happened... i felt a similar way...
In this case i found nothing untoward with the bike..
Root cause was again my reaction to a stimulus, in this case a massively strong and directed crosswind.....

BMC TM01, Medium Large
I would have to measure equivalent stem length, it's a bunch of BMC parts you put together to get the right length & drop.
Profile Design ProSvet aerobar
Descending at 68km/h.

Had everything checked immediately after, no problems found

It's a bit silly to say that an instability has nothing to do with natural frequencies and is due to a bifurcation.

A bifurcation is math-speak for a 'forking' of the solutions of a system as a function of certain parameters, and within this function lies some natural frequncies inherent to the system. The complex conjugate pair comes from underdamped solutions of a system, since the discriminant is less than 0.

In airplanes you get coupling between roll and yaw resulting in certain instabilities of various magnitudes, and you can also have what's called pilot induced oscillations, where some delay in reaction and overshooting response creates the instability. In cycling, there may be both contributions in any given case of 'speed wobbles'. I would suspect rider delays in balance in response to some lateral road disturbance as the main culprit though.

Bifurcation does appear to be a better description of the phenomon than resonance. If speed wobble is a resonance, then it would happen at a variety of speeds if the bumps in the road were at a certain frequency. And it would also go away when you went even faster. But there are people that experience consistently at a certain speed no matter the road surface and also it just gets worse and worse as speed increases.

Now just like aerodymanic flutter, the stiffness and mass affect when it occurs even though it is not resonance. Also the riders inputs affect it, since a a large input near the critical speed will cause it to appear at a lower speed, once again showing the difference from resonance.

As my bike has carbon forks can I be involved to try and understand... like a few others since it has happened (twice on the same hill) i've lost all confidence on that section. On other descents i'm generally fine but naturally more wary. I did have one wobble before but that was pre fit and since then i've tanked it down that specific hill and been fine.

Bike is:

1. 2014 Trek Madone 2.1 H2
2. Bars are 40 cm Zipp Service Course 70 (replaced at the fit)
Stem is standard 10cm, i have an additional 3mm spacer in from standard but the stem was flipped to +7 degrees.
3. Descending a long steady hill. It's about 800m length total, shallowing out in the last third. On both occasions I was about mid-way down when the whole front end went wobbly on me, moving from hoods to drops, out of saddle etc seemed to make little difference. Controlled braking and the hill stopping bought things under control. The road surface was a little broken up but the second descent was during a triathlon and several people flew passed me without issue. I had pedalled at the beginning but had moved the pedals to level on the horizontal and tucked forward.

As I said above, all confidence lost on that descent now :(

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http://www.tritriagain.uk

it's often a combination of parts, I would not lose sleep over it. You can stop it by standing slightly to disconnect your butt from the saddle or stabilizing the top tube with your knees. Getting all tense and sighting the bike just makes it worse. It seems like some bike-wheel combinations just wobble for some riders. Sometimes.

That said I have had carbon, steel and aluminum bikes that wobbled, or didn't

I tried the bum off saddle bit but didn't quite have the mindset at the moment it was happening to try the knee bit.... i shall if i can pluck up the courage to try it again!!!

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http://www.tritriagain.uk

it's not uncommon to look around the group in a race on a fast downhill and see people contending with wobbling bikes. I even have a full suspension mountain bike that wobbles violently at speed if i take my hands off the bars, it's kind of amusing to do when riding with others

I wish there was something to blame like new technology, but alas. I think the light wheels we put on for races may have something to do with it.

My 23 pound Merckx MX Leader goes downhill like a coal truck

1. Spez Shiv Med
2. Zipp Vuka Bull, 1 spacer
3. sprint race down short step hill going 40+ and 2x at IMMT going 40+, scary as hell, and to pull out of TT position and move onto base bar and hold on for dear life with some light braking (I HATE braking going downhill). Both races was cold weather and legs were felling like noodles, not sure if that played a part or not?
-- have wondered if i went faster would it have gotten worse or better?
-- have Trek speed concept 9.9 size large now and have never gotten anything close to speed wobble on it.

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2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz

1. what kind and size of bike?
2012 Felt DA4
2. what's the front end config? stem length, # of spacers, and if a tri bike than the aerobar type
Fixed Length Bayonet Stem that came with bike
3. what were you doing when it happened?
Anytime I got the bike over 35mph on a descent the front end just became unstable and started to vibrate and oscillate. I thought at first it might be a wheel issue but after a few weeks of riding the bike I had to replace the frame with a DA1 frame (I crushed the DA4 frame into my garage when I forgot to stop and remove the bike off the roof rack....sigh). The DA1 frame was completely the opposite situation, it felt (and still feels) super stable on descents and I can stay aero up to 50mph without feeling any vibration or loss of stability. All the parts from the DA4 were transferred to the DA1 so it had to have been the frame.

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Underground Race Team
http://www.OURtri.org | Twitter | Facebook

2009 Felt B2R with stock bayonet stem and bars

Front wheel was a SRAM S80.

The only time I ever experienced it was on a practice run on the Keane descent the day before IMLP in 2010. It was shaking so hard I thought I was going to die--violent oscillations back and forth at about 43 mph. I've never experienced it before or since, whether with that wheel or with the stock wheel. I took of the S80 wheel for race day because I was so terrified.

Not the natural frequency of the bike frame. The natural frequency of the lean-steer oscillation mode of the bike-rider combination.

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AndyF
bike geek

I have heard that improper wheel dish can be a culprit with these oscillations as well. Example being, a properly dished front wheel matched to an improperly dished rear wheel.

Cheers,
G

2009 Kestrel Airfoil 47, stock front end setup (90mm stem, no spacers, profile T2 cobra aerobars)
Riding Recovery Loop with the womens, 34 mph on I think it was 121st street or wherever we turned off Ft Tejon. Whole fork vibrated, I hit the brakes, and the womens behind me also slowed up because it was really easy to see the wobble. Not so fun.

This is true. A bike frame would have a really high first mode by any practical set of constraints. The "lean-steer" oscillation is the roll-yaw (more like steering angle of front wheel) coupling that I mentioned, which is a property of the bike-rider system.

I'd love to know how long the stem, and the total quantity of spacers under the stem, including headset top cap.

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Dan Empfield
aka Slowman

54CM Cervelo P2C
Stock front end with a ZIpp 404 (non-FC), 6 deg 90mm stem flipped up, 20mm spacer
Bombing down a hill at 50+MPH on the bullhorns

Clamped the top tube with my knees and it steadied.

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Rodney
TrainingPeaks | Altra Running | RAD Roller
http://www.goinglong.ca

1 - quintana roo caliente, size M(54), carbon frame and fork
2 - stock cockpit for a 2008, vision aluminum basebar, aluminum extensions, 80mm vision sizemore stem, maybe 20mm of spacers
3 - going downhill, wobble started to increase in severity as i got close to 35mph, past 35 i had to sit up and use both brakes while bracing the top tube with my knees. at its peak, the wobble would have wrecked me if i had stayed in the extensions.

2008 QR Caliente, with forward seat clamp(i ride steep), two large water bottles in the main triangle, small saddle bag,
Real Design Supersonic 60(Zipp flashpoint rims - the hybrid toroidal aluminum rim/brake track, structural carbon fairing, Real hubs, bladed spokes), Continental attack/force combo, conti tubes, Shimano D/A 7800 drivetrain, FSA Team Issue Carbon crankset 170mm-50/34x12-28, pd-7800 pedals, selle SMP evo saddle

During the Solvang Century, there is one fairly long steepish hill where the wobble occurred. i was accelerating due to the steepness, so not pedaling. It really felt more like the interaction of the air coming off the front wheel and the downtube. i have come close to this at a slightly lower speed with these wheels on my s1(a 51) recently, and will see if the same happens when i build up my p2sl(also a 51).

i am about to rebuild the Caliente as a fixed gear.

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"...I try not to ever ride as slow as 20mph. ;) ... And even more than that, I don't race with a speedometer. My computer is set up to show Power // Cadence // Time. I don't actually ever know how fast I'm going. I only know that if I'm in 53/11, and it takes more than 100rpm to hit my target watts, it's time to coast." - Jordan Rapp on '09 IMC

1. Cervelo S5 58cm (2012)
2. 140mm/-17. What spacers?
3. It's not a one time event but almost any descent long enough to raise the speed to ~60kmh without pedalling. It could be just me but the front end is really nervous. Not the nicest bike in Tenerife...

Unfortunately i don't have it with me today (though it was a lovely day to have ridden to work!) if you can work it out from the picture that's the best I can do at the moment.

The stem i know is a 10cm Bontrager standard one (flipped as i'm not that flexible at the moment, so it's at +7 degrees)

The carbon spacer I do know is 3mm, and I presume the others are 10mm? No idea on the overall head size though - i'll try and measure it later....

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http://www.tritriagain.uk

1. what kind and size of bike?: 54cm KHS Flite Team
2. what's the front end config? stem length, # of spacers, and if a tri bike than the aerobar type: 120mm -6 stem, 15mm HS cap, no spacers
3. what were you doing when it happened?: Descending at roughly 40mph, road surface was moderately rough. This was the only time I've ever had wobbles on any bike, at any speed. I routinely hit mid 50s on this bike, the only thing I can think of that was different was that I installed slightly wider tires than I normally run. Clamping the top tube with my knees while lightly applying the brakes took care of the problem...

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"I'm thinking of a number between 1 and 10, and I don't know why!"

I have had speed wobble 4 times, and on 4 different bikes (53 cm round tube steel Masi Gran Criterium, 53 cm round tube Titus titanium, 1999 52 cm Kestrel Airfoil with early version of the Zipp 404s, Reynolds Aero fork, 100 mm built in stem on Profile Carbon x bars with 2cm of spacers, and 2012 52 cm BH Aero with 60 mm stem, no spacers, and first-generation HED one-piece aero bars). The bikes have been different, but the conditions are always the same: Speed over 40 mph (descending, of course, always on a straight descent, sometimes with cross-winds sometimes not), "unsmooth" or "bumpy" pavement, and light weight rider (me, 140 lbs). With the steel and titanium bike, the wobble cam under control once the speed dropped back under 35 mph or so, but with both carbon tri bikes the oscillation kept going until I go the speed down to about 12 mph. Used the "knee squeeze" technique and a lot of praying in each case to survive the wobble......
The combination of speed and bumpy surface seem to be the trigger for me.

I want to clarify that all bifurcations that result in oscillations exhibit resonance, but not all resonance is the result of a bifurcation. A non-resonating bifurcation would be a system that has several stable solutions; a stalled airfoil may have a stable, lower, lift coefficient that requires a lower angle of attack than initiated the stall to reattach. An example of a resonance that does not arise from bifurcation is a simple pendulum.

The example you give of a rider and road frequencies is not valid because it assumes that only forcing frequencies that match a natural frequency can initiate oscillations. A disturbance need only exist to destabilize a system and that system can oscillate about a stable mean with constant, growing, or decaying amplitude.

As a model that assumes the rider's hand's aren't directly creating the destabilizing steering response, this would mean that the rider's torso behaves as a damped upside-down pendulum that is cantilevered over the front tube and pivoted at the seat. This is more accurate the less input there is from the rider to the cockpit. In a limit, assuming a very stiff rider with no hands on the cockpit, there will be no phase difference from top tube to rider torso and the rider will follow a yawed path into the ground. Once the rider's torso is free to respond to a disturbance, the cyclist-bicycle system may oscillate.

Slowman's article states that we don't really know the cause of "speed wobble," but vehicle dynamics theory is advanced enough to tackle the problem for the cyclist-bicycle system with rigor. I'm sure this stuff is out in journals or books for motorcycle vehicle dynamics.

Just experienced my first speed wobble yesterday.

1. 2015 Felt DA
2. Felt alloy bayonet 2 bar with 3t ski bend extensions
3. Descending on a fairly regular route that I ride, but this time was my first ride on race wheels with 20-25mph gusts. I was demoing a set of 404's and it seemed like the wind couldn't decided which side of the wheel it wanted to take. The gust shot straight up the hill as I was descending. I was ready for it to happen but didn't expect it to be so violent. I went right for the rear brake and that seemed to do the trick.

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marceves.com

fortunately, you know what to change in the system to make the problem go away. and you found out before having to purchase it.

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Dan Empfield
aka Slowman

I used to get the speed wobble with my 51cm cervelo on fast descents. I never figured out what caused it but I can say that the same thing happened with a motorcycle I had where I changed the triple trees and altered the rake and trail. So I wonder if positioning and stem angle had something to do with it.

i wrote about speed wobble recently. in my own experiments it's not trail or steering axis related. it's mostly stiffness (specifically the lack thereof) related. stiffness of the system.

one aggravating element is a mass cantilevered away from or above the frame. this makes me wonder whether the fulcrum about which the bike vibrates is not in one place (steering axis, seat tube) as a lot of folks have speculated, but whether the fulcrum changes based on the offending element you add that contributes to the vibration. but i don't know. just, i've ridden bikes with very low trail numbers that do not vibrate at high speed, or any speed, because the system is so stiff.

you mention it was a cervelo that wobbled and, ironically, it's a cervelo (R3) that i used to conduct tests on how small the trail could be and still have the bike be absolutely reliable and wobble free at any speed.

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Dan Empfield
aka Slowman

1. what kind and size of bike?
colnago C40 (scarey wobble thought I was going down) and moda echo (minor wobble, stiifer bike) same place.

2. what's the front end config? stem length, # of spacers, and if a tri bike than the aerobar type
3. what were you doing when it happened?

I was gong down the same scarey descent
common factor was a side/tail wind and heavy breaking at speed >40mph
I have gone down fast descents with the C40 at over 50mph but more relaxed and no breaking, The yorkshire dales are frightening/dangerous at times.
There where people passing me at what must have been 60mph no wobbles from them. I can only say the wobble is due to the wind and heavy braking causing resonance.

In both the Dales and Peaks I have had issues with wobbles in moderate to high winds on both a Tri (spec Transition) and road (spe Amira) bike when riding with 40mm carbon fairing wheels but not with standard training wheels. I think this is because in windy conditions the carbon wheels place additional force both out front and behind the rider+bike system, roughly analogous to placing lots of weight far infront or behind the rider. Adding force in these areas seems to help overcome the stiffness of the frame and allow the resonance to build. I suspect that braking can make things worse because the localized force of the brake pads further destabilizes force distribution across the wheels/system which can amplify the dominant resonance. I imagine some of the benefits of increased frame stiffness have been lost by the proliferation of aero-carbon wheels introducing another pivot point on resonance in the system.

Scott plasma 10
90mm stem
1cm spacer

Second time but last time was 20 years ago. 40mph downhill, I was sitting up, enter an open area with crosswind and the death wobble started. Had on a set of Chinese 60mm carbon clinchers that I only have a few rides on. Older style V shape not the wider U shape. Older tires as well. Scary!

Trek speed concept XL
Tall stem
It’s happened on ZIPP 808 and bontraeger Aeolus 9 wheelsets
It’s happened 3 times and definitely a death wobble. Thought I was going to die. Only happens above 40 mph usually around 45 when out on the bull horns with my hands on the brakes. Coming downhill if I catch a crosswind. Now I feel like I anticipate it and can brake and ride it out, but still scary as hell.

You resurrected a super old thread, and the only reason I'm answering is to tell you that if your Speed Concept is having speed wobble it is almost surely because the stem attachment bolts and/or one of the steering axle bolts are loose. This is super dangerous so you need to fix it ASAP. See the Speed Concept service manual (page 7) for the torque specs. You need to take off the bars to get inside to tighten the bolts.

Awesome post.😁

prattzc wrote:

You flew through his jet stream? Hasn't Goose's death taught you anything?

*jet wash

https://getyarn.io/...ad-bfa8-087d4fe3c755

Sorry, but as a guy who watched that movie several hundred times growing up, this is an important distinction

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

I had the same experience on almost the exact same setup, 2012 S5 VWDs in both 58cm and 56cm. 130mm stem on the 58, 140mm stem on the 56. No spacers. -17.

That bike was really bad in high speed crosswind descents. I switched from the S5 to a 2014 EVO High-Mod and moved everything over from the S5, including wheels. Duplicated positions. Speed wobble went away. I have 19K miles on the EVO and zero speed wobbles. So while there would be some subtle confounding factors at work, I feel fairly confident that the S5 was just susceptible to speed wobble/shimmy.

Specifically, I think it was the flexy head tube that was primarily to blame. It was super skinny and felt "flexy" to me. Sure enough, when the next version of the S5 came out, the first thing Cervelo touted was the stiffer head tube! Maybe if Damon's NDA is expired, he can finally come on here and say, "Yes, OK, I will admit it, the flexy head tube was the REAL reason that our pro riders wouldn't ride the old S5 on mountain stages"

:-)

Here are three examples I caught on video:

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


This one is shorter, happens at 2:00:
https://vimeo.com/50805571


This one happens at 13:30:
https://vimeo.com/78044849

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

At the time I was running the 2012 S5 and getting lots of shimmy/wobble, I had a 2012 R5 that was set up identically (this was easy enough to do as the bikes shared geometry). Zero shimmy/wobble on the R5. Which supported my theory that it was all due to the noodly S5 head tube/front end. The R5 was rock solid.

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

Thanks!! I will check that immediately.

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?

I got a couple of speed wobbles last year and traced it back to the skewer. Specifically, I would get a speed wobble on my bontrager wheel set if my zipp aero QR skewer wasn't clamped super tight.

Never an issue with the OEM skewer on the bontragers. I also haven't been able to duplicate it with the zipp skewer on another carbon wheel set, not that I am trying to induce a death wobble....

Something to consider.

I've had speed wobbles a few times. Mostly fairly minor. Once or twice more severe. Once on a Ridley Orion rental bike descending Mount Teide in Tenerife. Others on my Canyon Ultimate CF SL on various descents, typically with slightly uneven road surfaces and doing speeds between 60km/h and 80km/h. A knee to the top tube generally damps it quite quickly. I've never needed to slow down that I can remember.
It seems fairly clear to me that the cause is simply a positive feedback from the rider in response to an initial perturbation. The bike is disturbed to the right, the rider is left behind and this causes a slight pull to the right handlebar. The rider corrects but the pull on the handlebar has increased the amplitude of the movement at the front end, ensuring that the rider cannot coordinate the correction accurately and the bike swings back the opposite direction with a similar positive feedback so that the amplitude of oscillation is maintained or increased. Bracing against the top tube removes much or all of the coupling between the bike movement and the positive feedback due to rider movement and the oscillation subsides.

I was doing 40-50mph down a long straight hill in yorkshire. scared me to death almost literally. I had no control of the bike and for 20-30 secs I thought I was going down flat on my face. The only saviour was that the road was long and straight if i had to negotiate any bends I was a gonner. It was terrifying. as the grade subsided from 20-25% to around 10-15% I mustve slowed a bit and the wobble stopped.
There may have been a cross wind and I was riding a colnago C40 10cm stem it was the first time and last I had experienced it with this bike even though I have gone 50mph on it before.

I suspect the wobble had something to do with the cross wind (wheels I cant remember exactly but they where nothing special low rim alu )

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.

That's interesting, I hadn't heard that before. Any link you might of read and can share where that is discussed with data?

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?

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.

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.

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.

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Amateur recreational hobbyist cyclist
https://www.strava.com/athletes/337152
https://vimeo.com/user11846099

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.

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"They're made of latex, not nitroglycerin"

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.

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.

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.

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.

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.

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

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

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

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

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

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Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

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.

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.

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

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.

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.

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