General rule of thumb to keep a reasonable footprint is the section width of the tire should never be more than 2" wider than the wheel it's mounted on. 225 is the section width of the tire in MM. The 10 hole is 7" wide. 7 + 2 = 9" maximum section width. 9" X 25.4 (mm/in) = 228mm section width. So, you really shouldn't exceed 225/235 on a 7" rim if you want the tread to actually stay on the ground across the full width. While people mount much wider tires on them all the time, they may be fooling themselves with regard to the effectiveness of that approach. 245 tire needs at least a 7.5" wheel. 255 needs 8" wheel - you can do the rest of the calculations using the info above.