guys, in about 3 days, im gonna go buy myself some new rear tires, because the ones i have in the back are 235/40/18 and they hit on the body..

and in the front i have 215/35/18 and well, the front never hits the body, and infact if i put a straight ruler, the ruler, can go thru touching the tire, and under the body, without touching the body, but in the back it hits the body.. so obviously the tire is too big,

can anyone tell me what a good size is for the back? or should it be able to clear it if i was to get 215/35/18 on the rear also?