Help - Vibration from Front Wheel

[peetbee]

Hello, I've got a Yamaha XJ650 and it's got a weird vibration that is at it's worst at 40mph, (tries to waggle the bars). Below 40 it seems ok and above 40 it gradually gets less and less until it's unnoticable at 70.

The wheel's been balanced, it's got new wheel bearings and the rest of the bike is in good nick. Has anyone got any ideas of what to check, could it possibly be the tyre itself?

Any help appreciated as it's making me feel a little nervous. Thanks

[Andy Oh]

I'd get it balanced again just to make sure and to eliminate whether the wheel is balanced properly

[Carrera2]

Have you lost a bar-end? If you have it's probably the cause...if not then I can't help other than to suggest getting the wheel balanced as suggested.

[morrisman]

Hi all, first post on Pistonheads, so I have to jump in somewhere:

Make sure your tyre is not deformed, bulging or mounted incorrectly, give it a spin and make sure it 'looks' true as it spins. Also eyeball the wheel rim for the same things.

[black-k1]

What tyres have you got on the bike and is the front well worn? I used to have a BMW that ran on Metzler ME33 fronts which had a "block" type pattern. When the front tyre got worn the bike would "shake the bars" between about 20mph and 40mph. Sometimes this would be bad enough that I was convinced I had a puncture.

[zzr]

Also check the brakes aren't binding slightly.

[mtbr]

Petebe,
The fact that your wobble occurs around 40 mph and goes away as speed increases, suggests it's probably due to the natural castor action of the front wheel / rest of the bike behind the front wheel.
All bikes do this at a critical speed, usually around 35 to 40 mph, although bike manufacturers do their best to minimize the effect by careful tuning (and mostly it's almost unnoticable).

All wheels running with castor have a critical speed at which they are unstable. It's the same effect that causes a supermarket trolley's wheel to flutter like mad if you push the trolley fast. Any weight carried high on the rear of a bike tends to exagerate the effect. Do you have a top box on the bike?

It would also be worth checking your steering head bearings for any wear/slack as that can also make the wobble more apparent.

Mark

[peetbee]

Thanks for the advice, I'll get the balancing checked again this weekend. The tyre has plenty of tread (can't remember the brand, but I know it's not the same as the rear), I'm not missing a bar end and the steering head bearings have been checked and declared fine too. No top box on it either.

It's all a mystery! I will get the wheel checked over again too to make sure it's ok and the brakes (they seem fine to me) and see if there is any improvement. It rides fine most of the time it's just really unnerving in a 40mph bend.

[black-k1]

peetbee said:

... (can't remember the brand, but I know it's not the same as the rear...

That might be the problem. There may be a compatibility issue between the front and the rear. May be worth fitting a matched front and seeing if the problem goes away. If it doesn't, then you can always re-fit the current front when the new one wears out.

[desmo]

when was the last time you replaced the fork oil? poor dampening can allow the wheel to bounce too much which may be felt on the bars, does road surface have any effect on the vibration. Check the rear wheel balance too, you could be tranmitting the vibration to the bars, if you relax your grip a little, does it get worse or better?

[peetbee]

Sorry for the delay in updating you all, I know that you've been on the edge of your seats wondering if I got it sorted!


But the prize goes to Black-k1, twas indeed a dodgy front tyre, we think it must have been standing with a soft or flat front tyre for some time before I bought it which deformed the carcass slightly - you couldn't really tell but in an attempt to balance it it took about 3lbs of weights, well ok maybe not quite that much

So new tyre to match the new rear and no wobble

Thanks for all the advice, and for those of you who park your bike up for long periods please check your pressures and possibly even rotate the wheels every now and again to stop the same happening to you.

[black-k1]

Great to hear its all sorted! It also reminds me, I must remember to check the pressures and turn the wheels on my bikes tonight!

[morrisman]

peetbee said:

Sorry for the delay in updating you all, I know that you've been on the edge of your seats wondering if I got it sorted! But the prize goes to Black-k1, twas indeed a dodgy front tyre, we think it must have been standing with a soft or flat front tyre for some time before I bought it which deformed the carcass slightly - you couldn't really tell but in an attempt to balance it it took about 3lbs of weights, well ok maybe not quite that much So new tyre to match the new rear and no wobble Thanks for all the advice, and for those of you who park your bike up for long periods please check your pressures and possibly even rotate the wheels every now and again to stop the same happening to you.

Hmm, remember this post, the one before Black-k1?

morrisman said:

Make sure your tyre is not deformed, bulging or mounted incorrectly, give it a spin and make sure it 'looks' true as it spins. Also eyeball the wheel rim for the same things.

Not trying to steal the limelight, but when the crates of beer are bought in extreme gratitude just let me in at the front of the queue

[black-k1]

morrisman said:

Hmm, remember this post, the one before Black-k1?

Have just re-read the full thread. Free beer does indeed go to morrisman.

[peetbee]

Oops sorry!