Just purchased an 03 G35 coupe with axis halo 18" wheels on it. The sizes are 18 x 8.5" on the front, 18 x 9.5 on the rear, with 245/40/ R18 tires all around. They look great on the car, but the guy who had the car before put adaptors on the rear that make the wheels stick out in the back, to the point where if I go over a bump too fast the tires on the rear will go up and touch the bottom of the fender (not wheel well). I want to get adaptors thin enough where they can clear inside the fender, obviously much safer that way. Any idea what size I need?

Can't answer that question without knowing the offset of the wheels.