Speed Wobble!

[Trickedem]

I experienced it when I was touring in Spain a couple of years ago. This was on my steel framed tourer, whenever I went over 25 mph it started to occur. This was definitely down to the weight distribution with two heavy panniers on the bike. I know this because I regularly do over 35mph on the same bike when riding it to work. I figured that if I do a tour on this bike again, I will get a couple of front panniers to even the weight out.

 

[Dogtrousers]

I saw it happen to a friend of mine riding down a long incline in the Brecon Beacons. I thought he was messing around to begin with. We had a couple more long inclines in that ride but it didn't happen again, possibly because he was being more cautious as he was a bit alarmed by the whole thing.

@Dirk Thrust that's an interesting video. Which one were you?

 

[Dirk]

@Dirk Thrust that's an interesting video. Which one were you?

Now, that would be telling!

 

[flatflr]

Had my first speed wobble on Saturday's ride. 2nd ride on my new bike (carbon frame with brand new wheels), descending a small slope I got up to 33 mph and it started (a very brown moment). Just happens that i'd read this thread a few days before and remembered to grip the top tube with my knees which stopped the wobble. I'm sure it's not the bike but going to give the bike shop a call and will pop it in to get them to check it out just in case.

 

[Fab Foodie]

Had my first speed wobble on Saturday's ride. 2nd ride on my new bike (carbon frame with brand new wheels), descending a small slope I got up to 33 mph and it started (a very brown moment). Just happens that i'd read this thread a few days before and remembered to grip the top tube with my knees which stopped the wobble. I'm sure it's not the bike but going to give the bike shop a call and will pop it in to get them to check it out just in case.

99% certain it's likely to be tense rider on new bike, but no harm having bike checked.

 

[flatflr]

Is probably that I was quite cautious as it's a new bike after trashing my last one after crashing when I hit a pot hole (2 weeks off the road, twisted rear wheel, badly scraped frame and badly sprained ankle).
Has thrown my confidence a bit.

 

[Fab Foodie]

Is probably that I was quite cautious as it's a new bike after trashing my last one after crashing when I hit a pot hole (2 weeks off the road, twisted rear wheel, badly scraped frame and badly sprained ankle).
Has thrown my confidence a bit.

It can happen!

 

[HLaB]

The only noticeable speed wobble Ive had was on the flat and it was probably more to do with my weight balance. Sprinted up to just over 30mph in a tt finish in the clip on bars when suddenly the front wheel started to wobble uncontrollably. I thought s0d it and decided to sprint through it, felt like the whole bike would fall apart

 

[Ajax Bay]

Link to 'Steering!' thread??

 

[raleighnut]

Link to 'Steering!' thread??

No, the 'Speed Wobble' is more to do with resonant frequency and if you try to control it through steering it gets worse Also the more stiff a frame is then the more susceptible it can be to doing it, my 531c Road Ace can be a beggar for it and conversely slackening the 'death grip' on the handlebars normally cures it on that as does laying one leg against the top tube.

 

[Yellow Saddle]

No, the 'Speed Wobble' is more to do with resonant frequency and if you try to control it through steering it gets worse Also the more stiff a frame is then the more susceptible it can be to doing it, my 531c Road Ace can be a beggar for it and conversely slackening the 'death grip' on the handlebars normally cures it on that as does laying one leg against the top tube.

I think it is a valid link and connection to make.

The speed wobble resonance appears to be a circular steering reaction that cannot be arrested because the system's resonance bounces the action back and forth. Resonance is difficult to pinpoint and predict because of so many contributing factors, but I got lucky, I think.

I've had a bike that always shimmied at 46kph. I had a route with a long downhill of a gradient perfect for allowing me to approach the shimmy point relatively slowly. I could predict the onset and control it by either slowing down (but to a point way beyond it's initial start point) or by destroying the resonance's node. This node seems to be the seat and by standing up I could instantly arrest the shimmy. I got very good at it and eventually could do it no-hands and no-hands standing up. In the latter position I had to clamp the seat between my thighs and for those interested, it did not stop the shimmy. My theory is that it didn't destroy the node.

By the time I moved away from the area I must have repeated the exercise 30 or 40 times. My mates got bored with my tricks and musings and bored with having to wait for me at the bottom of a very, very long gradient that just asked for free speed.

I got double lucky in my amateur analysis of the problem. I had a Cannondale CAAD4 at the time. However, I had an exact geometric replica of that bike made from steel. The reason for that was that I wanted to build my own bike after I purchased a jig from a framebuilder who went out of business. I ordered a set of tubes from Ceeway and because I had no experience with designing frames, I simply copied my Cannondale's angles and tube lengths.

The equipment on both bikes weren't exactly the same though. The one had 28-spoke wheels, the other 32. The groupset was also from different eras albeit the same brand and level. Stem and handlebars were dimensionally the same but brandwise not.

Only the steel bike shimmied at that speed. I never managed to find a speed at which the Cannondale would shimmy although, of course, given the right conditions and load it would shimmy somewhere this side of the speed of sound (my maximum on a good day).

Although it is extremely difficult to really say, I could swear that I could see the stem swivel left and right, exactly like counter steering. Hence my theory of counter-steer bouncing backwards and forwards within the frame's boundaries of flexibility.

 

[Proto]

In the motorcycle world known as a Tank Slapper. One of my Fireblades was prone too it. Never got me in trouble, unlike this poor fellow (also on a Blade, I believe)

 

[Gert Lush]

Never had speed wobble on my bike but had it a fair few times when I used to skateboard.

 

[Fab Foodie]

http://www.sheldonbrown.com/brandt/shimmy.html

 

[Banjo]

Interesting that the motorcycle video suggests that a worn rear tyre with a new front tyre could be the worst combination. My bikes are often like that.