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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

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.

28 comments

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cyclisto [222 posts] 4 months ago
3 likes

The knee thing is very effective indeed

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beezus fufoon [672 posts] 4 months ago
0 likes

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

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DavidC [157 posts] 4 months ago
1 like

Do not lift your weight from the saddle. That is very dangerous advice. It significantly reduces the damping of the frame (which is what knees on the top tube increases).

Clamp the top tube with your knees, as far forward on the top tube as possible and as tight as possible, and slow down. 

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Podc [83 posts] 4 months ago
6 likes

Only had it once. I shifted my weight back and it started. Not sure if it was the lifting of my rear end, the shifting of weight rearward, or the extra weight I put on the bars as I moved that triggered it.

Almost shitting my pants seemed to sort it.

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Mat Brett [651 posts] 4 months ago
0 likes

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." 

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beezus fufoon [672 posts] 4 months ago
1 like
Podc wrote:

Almost shitting my pants seemed to sort it.

so erm, is it "unloading the saddle" or unloading in the saddle? 

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wycombewheeler [1103 posts] 4 months ago
5 likes
beezus fufoon wrote:
Podc wrote:

Almost shitting my pants seemed to sort it.

so erm, is it "unloading the saddle" or unloading in the saddle? 

Try the first one first, then move onto the second one.

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DavidC [157 posts] 4 months ago
3 likes
Mat Brett wrote:

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

Jobst Brandt is wrong.

Read how he did his research – initiated shimmy on a bike which tends to shimmy (how he created an environment to test his methods) is not the same as a normally stable bike entering a violent oscillation.

Many years ago I had a road bike for which, when riding no-hands, a slap on the side of the stem would cause shimmy. Fun and games, oooh look at me, then hands back on the handlebars and it would stop – a simple solution to an soft oscillation. A few years ago, after installing new wheels on a different, faithful, road bike, I experienced very hard shimmy twice within a few weeks on mountain descents. Unweighting the saddle caused the amplitude to increase dramatically (the frequency remained the same), the shaking bike almost throwing me off. 

Both bikes had shimmy, but the two situations and their solutions are not comparable. Brandt's methods were flawed, his advice bad.

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fullers1979 [60 posts] 4 months ago
3 likes

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! 

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FatBoyW [232 posts] 4 months ago
1 like

The whole thing with speed wobbles is not clear to me.

One thing I have noted is that, for me, confidence is a factor. I have watched nervous descenders get a 'speed' wobble at crazily low speeds just because it is  downhill.  I have assumed this is because they are very tense with tight shoulders and gripping the handlebars. (I've tried it and it can be scary!

If you keep your shoulders soft and elbows bent and hold lightly on to the handle bars - all is good the when not pedalling getting your weight balanced on the pedals off the saddle. Then a bike will hold line. I find keeping the saddle touching thighs and if nervous a knee touching top tube is best.

I know from my own experience it is when I have been nervous descending that I have had  speed wobbles. Basically had a bad fall (not off a bike!) and was riding mountains with barely healed ribs, verterbrae etc. Once I had given myself a good talking to and relaxed I returned to fast (50mph) and enjoyable descending!

Oh and I find the knee touching the top bar is a great tip for stability which you can do whenever you feel a little nervous.

Look at the pros - bring both knees in; getting your head in front of and below the bars; hands each side of stem; flat back; feet flat and cranks horizontal  can attain some mean speeds!  yes it is not the safest with your hands and head in that position but it is fun.

Anyway the point I wanted to make is the main issue seems to be nerves - if you think it could happen then you automatically tense adn trouble starts...

 

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wellsprop [244 posts] 4 months ago
0 likes
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)!

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Spacer [15 posts] 4 months ago
2 likes
DavidC wrote:

A few years ago, after installing new wheels on a different, faithful, road bike, I experienced very hard shimmy twice within a few weeks on mountain descents. Unweighting the saddle caused the amplitude to increase dramatically (the frequency remained the same), the shaking bike almost throwing me off. 

Yr experience is the opposite of what is reported by people in many places. http://www.slowtwitch.com/Tech/Speed_Wobble_5033.html https://cyclingtips.com/2011/03/speed-wobble-when-the-bike-shakes-its-head/ http://forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/Triathlon_Forum_F...

'Unweighting the saddle a bit makes the system more flexible, decreasing the natural frequency to one that's lower than your current speed. The shimmy stops' – Damon Rinard, Engineering Manager, CSG Road Engineering Department, Cannondale & GT Bicycles (ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

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BlindFreddy [7 posts] 4 months ago
2 likes

Had a bicycle that I could induce wobble on which allowed me to experiment. Knees clamping the top tube was of modest benefit. Best result was to unweight the saddle move my bottom as far behind the saddle as possible - shimmy stopped immediately. I presume that the change in centre of gravity changed the natural harmonic out of the self reinforcing shimmy range.

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therevokid [1013 posts] 4 months ago
2 likes

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

forward a little and the shake went away !

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DavidC [157 posts] 4 months ago
1 like
Spacer wrote:

Yr experience is the opposite of what is reported by people in many places. http://www.slowtwitch.com/Tech/Speed_Wobble_5033.html https://cyclingtips.com/2011/03/speed-wobble-when-the-bike-shakes-its-head/ http://forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/Triathlon_Forum_F...

Honestly, a lot of what is written about bicycle shimmy is rubbish. Many people talk about headset adjustment (the difference in resistance and damping between a loose, tight or properly adjusted headset is miniscule, really, with no change in bike geometry), frame construction and stiffness (why didn't many/most steel bikes shimmy on every descent?), and some write articles as if a frame can be designed and built which favours or resists shimmy predictably. There was one company which even announced a "cure" some years ago, an assymetrical fork — this has obviously not taken the cycling world by storm. 

The occurance of shimmy is a result of the total system, the complete build of the bike and the rider. This is why I was able to ride a high-end, stiff racing bike for several years in mountainous terrain and never have the slightest problem, and then with a change of wheels it immediately became an unstable monster.

As for unweighting the saddle, if it works for some people and doesn't work for others, then it is not a reliable solution to be recommended as the first course of action in what really is an emergency situation.

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tom_w [220 posts] 4 months ago
2 likes

I had a bike which would consistently speed wobble if a sharp gust of side wind caught the front wheel and I was also out of the saddle descending (which I tend to do automatically on bumpy descents from all the years on a mountain bike).  It scared the shit out of me.  I completely agree with those saying it's a function of the total system.  On that bike remaining seated stopped the wobble.

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audiobully [2 posts] 4 months ago
1 like

Another cause is poorly aligned brakes. I once had a speed wobble while descending at about 80kph. Turned out that the rear brakle caliper was slightly out of line so that when I touched the (rear) brake, it threw the rear wheel out of line and caused an horrendous wobble. Because it was caused by the brakes, it stayed until I eventually stopped. Before then, I could comfortably descend (I think 96kph was my top speed on one ride), but after that my confidence was shattered. 

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Chris Hayes [143 posts] 4 months ago
1 like

Avoid this simply by not shopping at Halfords 

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maviczap [56 posts] 4 months ago
1 like
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

 

Did you buy my Litespeed from me  1 Death machine

 

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maviczap [56 posts] 4 months ago
1 like

As above, my Litespeed Mira alu frame was prone to going into a wobble at plus 40mph speeds. First time was in the Pyrenees, pumped the tyres up and it didn't misbehave again. Because it was a compact frame, with a sloping top tube I couldn't do the knee thing.

Last time was descending Ventoux, hit a bump (same place as Guy Martin crashed in the gocart) and it went into the biggest shimmy I'd ever had, nothing would stop it, feathering the brakes, skimming off the speed slowly, bit of front brake, a bit of rear, shifting my weight, it carried on regardless.

I was preparing to bail out & I took my foot out of the left pedal & it stopped there and then. I must have been as white as a sheet.

The final solution, I got rid of it!

It had paper thin tubing and thin bladed forks, all of which I think contributed to having a front end that would go into a headshaking wobble. I read a few posts about this & other Litespeeds doing this.

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sw1sst [12 posts] 2 months ago
3 likes

This article saved me this afternoon. Descending quickly, hit by a gust from the side. Over the space of ten seconds went from steady descent to full on wobble.
Gripping the top tube with my knees instant fix. Thanks..

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Virtual [1 post] 1 month ago
0 likes

Had my first one today coasting into a bend at 52mph. Should have known better - first  time on upgrade wheels that are definitely twitchier and I think I tensed up and shifted my weight, unsettling the bike as I went into the corner. I somehow managed to save it without hitting the hedge but it lasted for about 50 metres.

Instict told me to just ease up without breaking and I just rode it out. I was really lucky. The mountain biker I overtook on the way down said it looked well scary from behind. I can confirm it definitely was!

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JClark63 [1 post] 1 month ago
0 likes

I've read and considered this thread carefully. Death Wobbles seem to be the ghost in the machine. There are no specific causes or complete fixes. 

At 53 years old I had my first real experience with this event on a hill I had ridden before. I did everything wrong. I tensed up, held a death grip on the bars, and grabbed my brakes. I thought I was about to become hamburger going down this roughly surfaced road at around 30 or 35 mph.

I've lost more than a little confidence just weeks before a 580 mile trip around Lake Ontario.

I wonder if the limited flexibility in my lower back contributed to the opportunity for the wobble to arise? I sit a little tall in the saddle. Add to it my undersized Fuji frame a trunk on the back end and I'll bet I might expect more of the same.

Any ideas on back flexibility would be appreciated (yoga is against physician's suggestion). I took care of frame size and now ride a Trek 720.

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CXR94Di2 [1700 posts] 1 month ago
0 likes

Don't go too fast and periodically apply brakes to shave of acceleration

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davel [1492 posts] 1 month ago
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JClark63 wrote:

Any ideas on back flexibility would be appreciated (yoga is against physician's suggestion). I took care of frame size and now ride a Trek 720.

Presumably there's logic to your physician's suggestion, so there could be an underlying condition that you haven't mentioned, so I'd go back to them and say 'OK, if not yoga, what?'. Personally I've found a bastardised version of yoga (the book 'yoga for cyclists') a useful source of a few stretches that I would never have tried.

But if something prohibits yoga, or stretching in general, the other thing to focus on is core strength. I'm a triathlete who doesn't swim much (or maybe bikes/runs too much), so that means I tend to binge my swim training and have frequent breaks away from it. It's great for nice and easy core strengthening - I always feel more stable on the bike during and after a swim binge.

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DaSy [753 posts] 1 month ago
0 likes

I have seen this caused on a few occasions by wheels, in particular the placement of a speed sensor magnet on a wheel. This is probably less common now, as many people are using GPS computers without the need for a wheel magnet but still, here is my experience.

It often happened with new wheels, which had a magnet installed by the rider. The natural instinct it seems, is to place the magnet opposite the valve stem, thinking it would balance the wheel.

In truth, most rims are pinned and welded at the opposite side to the valve hole, so is actually the heaviest part, adding the magnet puts a really out-of-balance point to the wheel.

I cured this issue on at least three occasions by moving the magnet round the wheel to the lightest part (found by letting the wheel settle after several spins in a jig, and finding the most favoured place to stop; lightest part will be at the top, or at least heaviest is at the bottom!).

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nniff [168 posts] 1 month ago
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My bikes occasionally do it, but infreqently.  My Plan A is relax grip on handlebars and shift your seat back a bit and grip with both knees on top tube, to calm the whole thing down and lighten the weight on the front (which is one of the things that is whipping the wheel back the other way).  If that doesn't work straightaway, Plan B is shift forward slightly and apply weight more on one pedal and brace other knee on frame - that changes the loading on the frame - more weight on the front, a twisting load from one side and a damper from the other - that stops it pretty much instantly if Plan A didn't work - ie two strategies - dampen and lighten the front, or load, twist and dampen.  The latter is scary, because you've got to try and change a position on a bike that has a different agenda and has already told you to eff off once.

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madcarew [379 posts] 1 month ago
0 likes

My impression is that 99% of the time it is rider. Maybe even higher proportion than that. I help a lot of beginner riders. Some get speed wobbles down a hill at 25 mph. They insist it's the bike. I get on the bike and ride it a t 25, 30, 35 mph down the same hill, go no hands.... no speed wobble. If someone says "some of my bikes do it" I'm sorry, it's inevitably the rider. I've been riding competitively for 30 years. I've ridden dozens and dozens of bikes, frequently over 50 mph. I have never had a bike give me speed wobbles since I was on a sit up and beg when I was 10 years old, except in one circumstance. If you want speed wobbles, simply unload the front wheel at speed down a hill. Sit far back on the saddle and lean back so there is little weight on the front wheel. You will get speed wobbles every time which will disappear as soon as you put load back on the front wheel. If you hold the handlebars with a death grip you may get speed wobbles on some bikes. Unclasping your hands from around the handle bars, leaning over the handlebars and placing your hands lightly on the tops will cure it, in my experience, 100% of the time.