unbalanced wheels?

[mattmbishop]

Hi there,
I'm having troubles with my XR650L, there's a low frequency vibration coming through when I'm on the road (not the buzz that these machines always make at highway speed). I thought it was loose wheel bearings, but I replaced them and the vibration is still there, although it's a bit better than it was. Now I'm thinking it may be the back tyre is unbalanced (as I think the vibration started when I last changed the rubbers) and the unbalanced tyre caused the wheel bearings to go out.

Is there anything else that could be causing such a vibration (it's about 2 hz at 50 km/h and seems to have a secondary frequency of about .25 hz)? Chain mis-aligned? loose swingarm? I don't have much experience with on-road work and I've never noticed a vibration like this on my trailbikes.

Cheers

[BMBaxter]

a worn chain and sprocket will create a pulsing,humming noise,most often noticable as a low vibration in the foot pegs.Loose engine mount bolts can also produce a similiar vibration.Also,a loose,or broken spoke would make a vibrating noise.My best guess would be the chain and gears.

[LordStig]

I'd second that - probably chain and sprockets. After the vibes start the chain usually starts to 'clank' as one or more links develop excessive side play. I usually take the clanking as a sign to change them ASAP - I had a chain snap at this stage, and it cause a fair bit of damage. Before you check anything further, check to see how much sideways play you have on your chain.

There are lots of other things it could be, though. Sometimes tyres wear strangely and cause odd vibes. Did you fit tyres you haven't tried before?

Stig

[mattmbishop]

I'm sure it's not the chain and sprockets, I replaced those not long ago.

I did change the back rubber not long before I first noticed the vibrations, and that was my best guess. I might put a new tyre on the back and see if that changes things.

Cheers guys