Using the measurements. For instance with my lift I know my max tire size was 31". But I went with 265/75 for the look which is a 31.6" tire. so to figure out how bad I would rub, without spacers, I calculated it out with the measurements of the inside and using the tire calculator to figure out the rest of the dimensions of the tire. Basically i don't rub unless i am turning the wheel to the extreme left or right, light pulling in/out of tight spots o_o