Cycling UK Forum

Help please I have what I can only call the whole bike shimmy or whip with increasing force, till I was lucky not to crash.I have had this happen three times in my life, years apart but the most recent was a week or so back. All have happend going down hill at 20+mph,the first was in heavy rain and wareing a cape and a strong gusting wind, the second on tour with only the back end fairly loaded and a cross wind, these two I had put down to the circumstances at the time. The last was in good weather light wind on an unloaded bike, but all on the same bike. I have checked the head set,running smothly,tyres and wheels in good nick and running true, frame seems inline ok and no visable cracks or faults but yes it is old now.Or is it maybe me? what ever It has scared the hell out of me to the point where I am unsure of riding this bike. Anyone out there had similar happen? or what else can I check, any advice wellcomed. eddie

There has been quite a lot of comment about shimmy and its many - sometimes mysterious - causes.

I'll just offer CJ's advice on dealing with it when it happens. Press one of your legs against the top tube and this will act as a damper to reduce and hopefully eliminate the vibration. Not necessarily easy to remember in the heat of the moment but a potential lifesaver.

Thanks mate,good thinking, thats the very thing thats saved me each time,that and relaxing my death grip on the bars, I thank god I too read it years ago eddie

I had a bad shimmy develop and spent months checking and replacing things.

In the end I discovered it was my rim failing and starting to fold over.
I failed to notice that when checking the wheel for trueness as I was checking the rim below the point where it was folding.

eddie wrote: . . . relaxing my death grip on the bars

It has taken me a very long time (years) to break out of the self-reinforcing "death-grip".

Meic, how does a rim "fold-over"? I've had a few crack along the circumference.

Pretty similar to your crack along the circumference. Only instead of cracking the very thin metal bent like a hinge.
So nothing broke but my normally 15mm wide rim was 17mm wide for a third of the circumference.

The knee into the crossbar is the best bet. But have you checked that the headset isn't loose? I had a series of shimmy incidentsa couple of years ago and once I retightened the bearings I had no more.

Not had this on a pedal cycle but have many years of motorcycling under my belt and it can be really scary at 70mph, believe me. Motorcyclists call this a t a n k - s l a p p e r and have endless discussions about the causes, most of which are not particularly relevant here, but one thing to look for which was explained by a respected motorcycle instructor relates to how you actually hold the bars: you say it is when going down hill particularly which makes me wonder how you are holding the bars and interacting with the bike:

Are you holding your arms straight and locked at the elbows as you make the descent (can happen as you ease up pedalling and lift yourself up for instance?) If you do this then every slight movement of your upper body etc. becomes directly and firmly fed into the steering (and that includes any forces from sidewinds for instance or due to reacting to jolts from the road surface) and you also stop the steering/forks geometry from self correcting as it is designed to do, then you end up trying to do it consciously and get into a fight with the bike.

The instructor showed how relaxing and becoming loose at the elbows allows everything to work properly again and yet you remain in control and able to do the steering thing using counter steering*. If you can control a Goldwing this way you can certainly do it with any pedal cycle so ease up on the death grip (as you noted) and do the Funky Chicken, i.e. bend you arms at the elbow into little wings and flap 'em (well ok the last bit is not strictly necessary but helps you to get it if you are a sixteen-year-old 'ped rider).

*Do cyclists ever discuss counter steering? It is another motorcycling topic that goes on and on and on with many never getting it.

niggle wrote:*Do cyclists ever discuss counter steering? It is another motorcycling topic that goes on and on and on with many never getting it.

Dont recall any discussions but been doing it as far back as I can remember. I discovered the technique for myself shortly after starting to go out and about on my first real bike. When I started to ride a motor bike I came across mention of it as a technique - previously I had just regarded it as something cool you could do when moving fast enough...

JF mentions this or something similar in Cyclecraft - the bit about avoiding being hit if an overtaking car suddenly turns left across you.

DaveP wrote:

niggle wrote:*Do cyclists ever discuss counter steering? It is another motorcycling topic that goes on and on and on with many never getting it.

Dont recall any discussions but been doing it as far back as I can remember. I discovered the technique for myself shortly after starting to go out and about on my first real bike. When I started to ride a motor bike I came across mention of it as a technique - previously I had just regarded it as something cool you could do when moving fast enough...

LOL, no offence but you discovered it when you learnt to ride a bike, you cannot get rid of those stabilisers without doing it, its the only way to stay upright! However I think you are referring to using it consciously, which is where improvements in handling the bike and avoiding hazards can be found.

niggle wrote::

Are you holding your arms straight and locked at the elbows as you make the descent (can happen as you ease up pedalling and lift yourself up for instance?) If you do this then every slight movement of your upper body etc. becomes directly and firmly fed into the steering (and that includes any forces from sidewinds for instance or due to reacting to jolts from the road surface) and you also stop the steering/forks geometry from self correcting as it is designed to do, then you end up trying to do it consciously and get into a fight with the bike.

The instructor showed how relaxing and becoming loose at the elbows allows everything to work properly again and yet you remain in control and able to do the steering thing using counter steering*. If you can control a Goldwing this way you can certainly do it with any pedal cycle so ease up on the death grip (as you noted) and do the Funky Chicken, i.e. bend you arms at the elbow into little wings and flap 'em (well ok the last bit is not strictly necessary but helps you to get it if you are a sixteen-year-old 'ped rider).

*Thank you for this one,I can not remember if my arms were locked or not, but I did have a stiff sholder from a fall on the ice a month or so back, and i did wonder if this was affecting my grip maybe. The rest fits too, jolts from the road and such like. I had gone over the bike a few times and found nothing, so me being the cause was a good chance, and I like the thought that our two groups, cyclists/motor cyclists have a lot in common. Long may your wheels turn and the wind be at your back eddie

niggle wrote:LOL, no offence but you discovered it when you learnt to ride a bike, you cannot get rid of those stabilisers without doing it, its the only way to stay upright! However I think you are referring to using it consciously, which is where improvements in handling the bike and avoiding hazards can be found.

Nothing there to take offence at - I was referring to conscious use!
I can't really remember details of learning to ride. I know it didn't involve stabilisers and did involve lots of hard dry playing fields and lots of wobbling

DaveP wrote:Nothing there to take offence at - I was referring to conscious use!
I can't really remember details of learning to ride. I know it didn't involve stabilisers and did involve lots of hard dry playing fields and lots of wobbling

Yes I cannot remember much either but then it was back in the 1960s, however I also never used stabilisers and have some vague recollection of borrowing the girl-next-door's bike, complete with balloon tyres and streamers coming out the end of the handlebars, and soon whizzing down the steep street we lived on in Yorkshire.

I can remember my fat auntie running down the street in her apron holding onto the saddle of my new bike on my birthday, just before my friends arrived for my party!