Newbie rim question!!

Hi guys, I just picked up a 1998 grizzly 600 today! It is awesome but the rear tires and rims are definately not the right setup. I have figured out that the factory tire size is 25x10x10, but i am having trouble figuring out what the offset of wheel i need is. Its a solid rear axle atv and the rims that are on it are more like what a front stock tire would be, so the tires are inset so far that the tire rubs on the exhaust and they just look weird. Can you guys help me figure out what offset wheel i need to order? Would a 12" rim be best to order with say a 3-5 offset? What is the stock rim offset on SRA atvs usually?Thanks in advance!!