most 12.5 wide tires a recomended to be mounted on a 10 wide wheel. The reason being it you mount a 12.5 wide tire on a 8 wide wheel it will pinch the tire in and increase the tire size. for example i hade a set of baja claws on my 99 dodge with an 8 wide wheel. the size on the side wall said it was a 33 12.5 15 but when it was mounted on the truck with air on a 8 wide wheel i used a tape to see the size and to stood at 35.6 inchs. 3 weeks later i went to a 10 wide wheel and the tire then when to 33.4 inchs when i checked it