i changed my stock tires to 225/50/17's with (>75% tread on them) about 7 months ago. i rotated the driver's side tires less than 1 month after i had the tires changed due to an improper wheel balancing. but here's my problem... i was checking my tires for how much tread i still have on them a couple days ago and the 2 front tires and the driver's side rear has about 60% while the passenger rear has about 40% tread. does any1 have any idea what is causing excessive wear on my 1 tire?