well, since i am guessing you have a 4man500s than you should be able to turn 28x12.5s in the rear with no problem...it may slightly bog in the thickest situations but my freind has a 99' 450 and it spins 28x12.5s rear and 28x9.5 front without a problem. i would not get the 28x10.5s because they are not as tall as the other 28s and do not have as good of a sidewall tread as the 28x12.5s. hope this helps