Jeep crew especially!! looking at 4wd tyre sizes, whats the story with tyres (tires?) sized like this: 31x10.5R15 ??? the normal 265/75/15 i can understand, but the other ones ? my brother recently bought a 97 Jeep Wrangler & enlisted my help in finding the biggest size tyre (sidewall especially) that he can fit on the factory 15 X 7 inch rims... please? sorry for being such a n00b.