there are several tire sizes available on any given rim sizes. (think about the "custom" cars these days with 22" wheels, the tire sidewalls are very short on those, and often you can get the same overall diam. as stock) I am NOT sayin to do something stupid like that with your camper just trying to make the point that rim size isn't "everything". If you go with a 4.80/12 it is shorter than a 5.30/12, and you can even go with something like a 145/12 like the old Geo Metros took. All "12 inch" wheels but alot of difference in overall height.