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What to do if your bike starts to shimmy

If you’ve ever suffered from a speed wobble you’ll know that it can be scary – very scary – and it can sometimes lead to a crash. So what can you do to control it?

Essentially, what happens in a speed wobble – sometimes called a shimmy – is that the front end of the bike oscillates, moving quickly one way and then the other, several times per second (the video above is from a YouTube user called Dean Magnusons). Your instinct in this situation is probably to grip the handlebar tighter to regain control, but the harder you grip the bar the worse it gets. Sometimes the movement is so bad that you’ll end up coming off the bike and that’s always bad news. 

What is a speed wobble?

There’s a lot of debate out there about what exactly is happening when you experience a speed wobble.

“Bicycle shimmy is the lateral oscillation of the head tube about the road contact point of the front wheel and depends largely on frame geometry and the elasticity of the top and down tubes,” according to the late US mechanical engineer Jobst Brandt.

“Shimmy is caused by the gyroscopic force of the front wheel whose tilt is roughly at right angles to the steering axis, making the wheel steer to the left when it leans to the left. This steering action twists the top tube and down tube, storing energy that both limits travel and causes a return swing. Trail of the fork acts on the wheel to limit these excursions and return them toward centre.”

Fellow bicycle expert John Allen doesn’t completely agree with Brandt’s views.

“Gyroscopic forces may play a part, but the mechanism is the inverse of how a fish propels itself through the water,” says Allen. “The sideways motion of the fish's tail at the back end of the fish propels the fish. In shimmy, the forward motion of the bicycle propels the sideways motion of the front wheel and fork blades. 

“As Brandt says, the flex of the frame in torsion brings the contact back to centre – but at the same time also causing it to oversteer to the other side. If you hold a bicycle over your shoulder and swing the front and from side to side, you can see how the wheel steers the opposite way. That occurs because the center of mass of the front-end assembly is ahead of the steering axis.”

The video above shows someone purposely inducing speed wobble (don't try this at home, kids!).

And here’s a typical example (below) of it happening spontaneously out on road. Notice how it starts at the handlebar and then affects the whole bike.

What causes it?

In our experience, a speed wobble is most likely to occur when:

• You’re travelling fast.

• You’re tense and/or cold, when a shiver might initiate it.

• You’re not pedalling.

• You’re riding no handed.

• The saddle is set high.

• The frame is long.

However, a shimmy can strike without all of these conditions being met; you can be pedalling along with both hands on the bars, for example. 

Some people say that speed wobbles are related to loose headset bearings or poor frame alignment, but we’ve seen no evidence to suggest that either are involved.

How to stop a speed wobble

If you feel a speed wobble coming on, we suggest the following:

• Try to stay calm; tensing up exacerbates the problem. Deep breaths. You can deal with this!

• Grip the top tube with your knees (if you’re pedalling, this obviously means you need to stop).

• Or lift your weight from the saddle very slightly, but don’t stand up.

• At the same time, although it may seem counterintuitive, reduce the strength of your grip on the handlebar. Keep your arms bent.

• Slow down. If you’re going downhill and this requires braking, gently squeeze the levers, don’t lock up the front wheel.

Gripping top tube knees 2 - 1.jpg

These tips have worked for members of the road.cc team. Some people have success by just laying one leg against the top tube rather than gripping it between their knees.

If you and/or your bike seem particularly prone to speed wobbles, you need to change something about the system (the bike or you). That might mean something as major as swapping the frame, but altering your own response in line with what we've suggested above when you feel a shimmy start is the logical first step.

Mat has worked for loads of bike magazines over 20+ years, and been editor of 220 Triathlon and Cycling Plus. He's been road.cc technical editor for eight years, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a past winner of the Cycling Media Award for Specialist Online Writer.

51 comments

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drewesq [10 posts] 1 year ago
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bike.brain wrote:

Had this a couple of times on the same bit of downhill on my road bike.  Found that moving my weight forwards slightly on the saddle stopped it.  Anyone else tried that?

 

Makes sense to me as you'll have more weight over the front wheel, which is what you want for control when descending

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basalt [1 post] 1 year ago
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I had a speed wobble on a moulton APB while using a Tri Bar. (Scott AT4) Irrecoverable, woke in ambulance...

I attributed it to the damping being unevenly applied, but perhaps it was just me...

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IrrelevantD [10 posts] 1 year ago
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beezus fufoon wrote:

it seems that certain set-ups get the death wobble at certain speeds on certain road surfaces - something to do with vibrational frequencies getting reinforced - coming down the pyrenees I was on an aluminium frame that did it at about 54kph every time - so speeding up was just as good as slowing down  1

The first time I experienced this was on an aluminium frame as well.  Everytime I got right arround 48-50kph it would start.  If I could get the nerve to get up to about 56 it would start to calm down.  After drifting into the oposite lane of travel on a descent durring a wobble it gave me such a stigma about going down hill I still get nervous going over 55kph.  This is over 10 years and 3 bikes later and none of my last 3 bikes have had the issue.  

The one thing I have noticed, as I have bought progressively stiffer frames, going from that old Trek 1200, to an 05 Tarmac, to a Giant Propel and now an Allez Sprint, the bikes have fealt progressively more comfortable at speed.  It makes me wonder if more compliant frames are more prone to the issue.

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BarryBianchi [418 posts] 1 year ago
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I've always found that shaving off some descent speed helps - it's never happened to me below 65 mph.

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HLaB [263 posts] 1 year ago
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I've had it I think twice on TT's I think.  Typically in the past I've stupidly saved too much for the finish and found sprinting on the tri bars wasn't a good idea.  First time I managed to power through it but the second time on another frame I wasn't as lucky.  Subsequently I googled it and would try the knee techique if it occurred again but touch wood it doesn't as i pace my self better on TT's  7

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PpPete [59 posts] 1 year ago
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Surprised you didnn't mention cross winds as a possible cause.

I have experienced shimmy on a couple of bikes. 
A steel tourer, which is very prone to it on any sort of fast descent.  But my best (Ti) bike only once, coming off the Pennines and getting hit by a sudden crosswind gust started it off.

I find single knee application - hard - against the top tube deals with it and feels more stable than trying to grip with both knees.

 

 

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Crazyhorse [6 posts] 1 year ago
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If you have excluded other possibilities, try replacing your fork. I experienced a pretty serious shimmy on my Lynskey Ti (and at lower speed similar though less aggressive symptoms) some months after a collision whcih superficially did not appear to have caused any damage. On replacing the fork, I have not had this problem -

However, unpredicatble and strong sidewinds at high speeds on straight descents can always cause problems, esp if you are not pedalling - so I try to keep my speed down in these situations now  1

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ColinF [1 post] 1 year ago
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Have experienced this on 3 different bikes all of which were good bikes. Definitely me and not the bike. Each time it has been because I have tensed up. Happened yesterday coming of a steep hill at 30mph and started to get nervous and tensed up because I could feel a cross wind pulling at me. As the video above shows this is very scary and I have came close to losing control which at speed is going to be nasty. Later descended another hill at 40 mph without incident but main difference was I stayed relaxed. If this ever happens again I will try gripping the top tube with my knees as recommended above but key thing is to stay relaxed and avoid it entirely.

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CXR94Di2 [2684 posts] 1 year ago
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it's probably a consequence of steeper head angles for lively steering. Get a bike/frame with longer wheelbase and slacker head angle.

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HLaB [263 posts] 1 year ago
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 I think I've had it twice two different bikes but the same thing stupidly sprinting on tt bars.  First time I sprinted through it but the 2nd time I wasn't  so lucky and lost a bit of  skin (fortunately the bike didn't even get a scratch.  I resist the urge now to sprint in the tt bars and touchwood it won't happen again  7

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OldRidgeback [3200 posts] 1 year ago
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wellsprop wrote:
fullers1979 wrote:

It's sounds very similar to natural resonance.

That perfect storm of all variables that will vibrate your bike at such a frequency that it will become uncontrollable. If it is this then changing those variables will generally stop it. I remember watching a video of a bridge swaying madly over a ravine in high wind. The answer to stop it was to add weight by loading it with trucks to change the bridges point of natural resonance. Although if you saw the vid any driver would've been mental to drive onto it! 

However back to cycling terms, if it is this, and I openly admit I am no expert (just adding my twopenneth) then any change in the state of the bike will change the point of natural resonance. Beit changing the weight or speed or changing the amount of flex in the frame (gripping the top tube with your knees) should make a difference. 

All that being said if you're calm enough to do any of this whilst travelling a high speed then more kudos to you! 

Yeah, the engineer in me agrees with the natural resonance. Putting your knee on it on the top tube damps the oscillation, similarly, I imagine reducing grip on the bars decreases the rigidity of the system and prevents the "over steering".

Scary stuff though, I managed to get a bit of a front end shimmy the other day when I went into a corner too fast and pulled on the anchors just as I entered the corner (which drops quite sharply)!

 

In my previous work as an engineer I did a lot of work on resonance. I was basically having to design components so that they would be able to function at very high rpm without resonating in such a way as to cause them to be damaged. A shimmy on a bicycle is a form of resonance. It's as simple as that. Anyone who tells you about gyroscopic forces does, quite frankly, not know what they are talking about. There are many, many variables that can cause shimmy in a bike. The rider's weight and weight distribution are two key factors, but also included are the frame design, frame stiffness, headset stiffness, tyre type (and tyre combination), wheel type, fork design... and so on. A bike that may shimmy badly at speed with one rider may not with another, basically because the two have different weights or riding positions. And two bikes of the same type from the same manufacturer may have different resonant frequencies depending on the types of tyre, wheel or headset stiffness, not to mention the riders of course.

Predicting what bikes will shimmy (or when) is really, really hard. If it happens, good luck. I've had a high speed fishtail on my bike when touring in the Picos in Spain as I made a very long descent. But it was a comparatively slow resonance and was fairly easy to control. A high speed headslap, now that's another thing altogether. Gripping with the knees should help. Shifting your weight might help, but might also make things even worse!

 

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MarkiMark [104 posts] 1 year ago
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Nothing to add really, except loosen your grip and slow down.

On a related note, I rode the RideLondon last Sunday. Following the hour and a half walk to the start line, during which I got colder and wetter, I eventually set off shivering. The first downward section into a tunnel had the bike wobbling like crazy because of my shivering. Miserable ride.

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henryb [90 posts] 1 year ago
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Mat Brett wrote:
DavidC wrote:

Do not lift your weight from the saddle. That is very dangerous advice.

Jobst Brandt: "Unloading the saddle (without standing up) will stop shimmy." 

I suspect that it's not reducing the load on the saddle that stops speed wobbles but rather that reducing the load on the saddle causes you to put weight on the front wheel, and it's that that stops the wobble.

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slappop [79 posts] 1 year ago
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"Your instinct in this situation is probably to grip the handlebar tighter to regain control, but the harder you grip the bar the worse it gets."

I've done a fair bit of gliding and this sounds similar to a phenomenon called "pilot-induced oscillation" (PIO). This is where you overcorrect and then overcorrect the overcorrection the other way, building-up an oscillation. (This can particularly affect trainee pilots while being aerotowed by a powered airplane.) The solution is to relax your hold on the control column and let the glider naturally stabilize.

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jaysa [151 posts] 1 year ago
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Glad I've never had a speed wobble - it sounds proper scary.

That's over 6+ road bikes, high/low profile wheels and a lot of descending at speed, which I love.

I'm usually relaxed descending, pinning the top tube with my knees like a jockey with a light grip on the bars, just letting the bike find its way ... or maybe just lucky so far  1

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DavidC [164 posts] 1 year ago
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a

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whobiggs [174 posts] 2 weeks ago
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therevokid wrote:

one of mine used to be the otherway around to Freddy's fix ... pull myself

forward a little and the shake went away !

 

I would agree, moving the weight forward is the best option but I guess there are many reasons for the wobble so the solution will most likely be different each time.

 

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whobiggs [174 posts] 2 weeks ago
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I've found releasing my fingers but keeping my thumbs braced helped ie stopping the natural push/pull effect of the deathgrip.

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mike the bike [1251 posts] 2 weeks ago
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I have found that a quick bowel movement solves this little problem.

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matthewn5 [1401 posts] 1 week ago
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Had a shimmy at 45mph going down Ballingdon Hill into Sudbury on the Dunwich Dynamo at about half past midnight. The bike had one of those big bikepacking saddlebags, which had made the front feel a bit light. Anyway, braking lightly and pressing knees on the top tube sorted it. Only ever had one shimmy before, in 54 years of cycling. The knee trick seems to work.

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Moist von Lipwig [156 posts] 1 week ago
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Funny this has popped back up, read this article the other year and it saved me when this happened to me coming down the Iseran at about 70kph this July. Took a couple of seconds to realise what was happening then what felt like an eternity to remember what to do. Weight off the seat and gripped the top tube with my knees and thankfully that worked. Was seriously shitting myself and thought I was definitely coming off. Don't want to go through that again.

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