Sounds like balance or alignment. New tire tread? Bead? Did you remove a rim lock?
Take a tape measure once and measure to the rear axle from a set point on the frame
Swing arm bolt center usually works. If its a bead you can usually spray some lube on it like Windex or soapy water, over inflate and roll it while hitting it. They normally correct that way. Im still wagering balance or more aggressive tread.
Danjal screwed with this post 08-23-2012 at 08:16 PM