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feature
QLsplX-r.jpgSpeed wobbles: try these 5 easy ways to stop 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.
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 been in cycling media since 1996, on titles including BikeRadar, Total Bike, Total Mountain Bike, What Mountain Bike and Mountain Biking UK, and he has been editor of 220 Triathlon and Cycling Plus. Mat has been road.cc technical editor for over a decade, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. 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 winner of the Cycling Media Award for Specialist Online Writer. Now over 50, he's riding road and gravel bikes most days for fun and fitness rather than training for competitions.
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55 comments
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..
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.
Avoid this simply by not shopping at Halfords
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.
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.
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.
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.
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...
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!
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.
so erm, is it "unloading the saddle" or unloading in the saddle?
Try the first one first, then move onto the second one.
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.
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.
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)
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.
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.
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
Did you buy my Litespeed from me
Death machine
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.
The knee thing is very effective indeed
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