Front wheel wobble at speed

[bobcolover]

I have a Challenge Fujin [ aluminium frame] and 3 times now have had a frightening speed wobble on fast down hills ; first at 42 mph, second at 36 mph , third at 28 mph. [I'm beginning to lose my nerve]
The front wheel bearings and spokes appear tight as are the back wheel bearings/ spokes. Headset also seems tight. Its over seat steering.
Its quite terrifying to see the front wheel beginning to oscillate from side to side at speed. I have been able to slow down; and luckily have not come off. I have hydraulic disc brakes front and back.
Tyres were properly inflated.
On each occasion I have had a single pannier on the left hand side. The pannier has not been especially heavy, clothes etc, and doesnt seem to affect lower speed handling.

Its almost as if there's some kind of 'harmonic ' in the wheel and frame set up that leads to the oscillation/ wobble.

Any ideas how to cure it, or has anyone else experienced a similar issue?
bob

 

[roubaixtuesday]

I think you're describing "shimmy".

I get this sometimes, particularly hands off.

It is a subject that divides opinion, but it's often recommended to put a knee against the top tube to stabilise, and I find that works.

I expect others will be along with different prescriptions shortly!

https://www.cyclinguk.org/cycle/shimmy-shock

 

[Ming the Merciless]

It is a subject that divides opinion, but it's often recommended to put a knee against the top tube to stabilise, and I find that works.

It’s a recumbent.

 

[bobcolover]

Therefore physically impossible. !!! well spotted Ming; but thanks Roubaix for the link etc; any help gratefully received .

 

[Tigerbiten]

On each occasion I have had a single pannier on the left hand side. The pannier has not been especially heavy, clothes etc, and doesnt seem to affect lower speed handling.

Its almost as if there's some kind of 'harmonic ' in the wheel and frame set up that leads to the oscillation/ wobble.

Any ideas how to cure it, or has anyone else experienced a similar issue?
bob

How much play/movement does your pannier have on the rack.
As a pure guess the "shimmy" starts with high speed air flow over/around the pannier.
This feeds back into/through the frame which sets up the resonance/wobble.
Try something like a rack top bag and see if it happens again.

 

[roubaixtuesday]

It’s a recumbent.

Ah. I had no idea from the post. But now I see which section. I'm an idiot. Thank you.

 

[bobcolover]

How much play/movement does your pannier have on the rack.
As a pure guess the "shimmy" starts with high speed air flow over/around the pannier.
This feeds back into/through the frame which sets up the resonance/wobble.
Try something like a rack top bag and see if it happens again.

I think the ' harmonic' starts in the flexing of the frame and may be magnified in some way by the front wheel, or a combination of the two. Theres not that much movement on the rear pannier; will check that out a top bag. thanks

 

[Ming the Merciless]

You might want to try putting an oring round the steerer fork inside the head tube. I’ll slow the steering down.

 

[bobcolover]

You might want to try putting an oring round the steerer fork inside the head tube. I’ll slow the steering down.

Thanks. Will look into it with lbs/bikefix.

 

[FrankCrank]

Shimmy can occur fairly often on tadpole trikes. On mine, the shimmy was resolved by adding 'stiction' to the steering system, with the addition of rubber washers to the ball joints. On a two wheeler, an o-ring added to the headset would achieve the same thing, as suggested above.
Easiest first step would be to remove the pannier and see what happens, then try the o-ring method.
In a worst case scenario, I have heard of folk fitting steering dampers, such as are available for motorcycles. Would seem like a sledgehammer to crack a nut in your situation, but is at least another option.

As you know, recumbents are a minority thing, and your low racer is a niche within a niche, and shimmy is a niche within..............etc.
Keep us posted on how you get the problem hopefully resolved, any info on this obscure issue will no doubt be appreciated by others who encounter a similar annoyance

 

[bobcolover]

Shimmy can occur fairly often on tadpole trikes. On mine, the shimmy was resolved by adding 'stiction' to the steering system, with the addition of rubber washers to the ball joints. On a two wheeler, an o-ring added to the headset would achieve the same thing, as suggested above.
Easiest first step would be to remove the pannier and see what happens, then try the o-ring method.
In a worst case scenario, I have heard of folk fitting steering dampers, such as are available for motorcycles. Would seem like a sledgehammer to crack a nut in your situation, but is at least another option.

As you know, recumbents are a minority thing, and your low racer is a niche within a niche, and shimmy is a niche within..............etc.
Keep us posted on how you get the problem hopefully resolved, any info on this obscure issue will no doubt be appreciated by others who encounter a similar annoyance

Thanks Frank; will see how i get on with suggestions and keep the thread updated

 

[a.twiddler]

A lot of steering damping comes from the weight of your hands on the grips. Some bikes will shimmy if you take a hand off, even if all the bearing adjustnents are right. If you have a folding stem, would it be feasible to adjust it so your bars come back a fraction (if it can be done without upsetting the fit)? This would have the effect of fractionally increasing the tiller effect, and might reduce or stop the shimmy. It might not, but could be worth trying. Even slightly wider bars, if yours are particularly narrow, could help. You also could try riding with your hands further out on the grips at times that you think the shimmy will occur, to see if that has an affect, before spending money on changes.

A bit of lateral thinking. A few years ago I fitted a sidecar to a motorbike I had, and the steering damper that came with it was shot. With standard bars the front wheel would shimmy alarmingly at low speeds. I tried fitting wider bars and the shimmy disappeared as if by magic, and I was able to dispense with the steering damper. It seemed to be due to the leverage and weight of my hands on the wider bars, and involved no effort on my part. It just ...worked!

So it might just be that a simple, seemingly insignificant adjustment might do the trick, no matter how illogical it might seem, before you get into taking things apart, fitting O rings, etc.

 

[bobcolover]

A lot of steering damping comes from the pressure of your hands on the grips. Some bikes will shimmy if you take a hand off. If you have a folding stem, would it be feasible to adjust it so your bars come back a fraction (if it can be done without upsetting the fit)? This would have the effect of fractionally increasing the tiller effect, and might reduce or stop the shimmy. It might not, but could be worth trying.

Thanks for the input; the stem is fixed on this model, although it looks like it should move, it doesnt. I am not sure where the 'O' ring should be fitted, I shall have to ask my LBS to fit it as I wouldnt be able to do that myself; does it go above or below the frame?

 

[Ming the Merciless]

I am not sure where the 'O' ring should be fitted

Below the top headset bearing race, inside steerer tube.

 

[bobcolover]

Below the top headset bearing race, inside steerer tube.

View attachment 783520

many thanks