How much ground height do you really lose running 18 in tires????I talked to a professional tire man and he told me for every 2in less round in tire you go down you lose 1/2in to 3/4in ground clearance....I didnt understand it but he started writing out math equasions and it started making sense....Some tire companies claim there tires are 20in when there really 21 or 22.....

well, youll have to know the actual diameter to know the actual loss of ground clearance. but if you assume a 20 is a 20 and a 18 is a 18, then you lose 1 inch of GC. its simple, you lose half the reduction in tire diameter in ground clearance, because if you drop 2 inches in tire diameter, one inch of that is above the axle, and one inch is below the axle, which lowers you one inch. of course to get it exact, meaure the real dia. of your tires now, find the real dia. of the ones you want, and divide the difference by two. and air pressure will affect it some too.