In my experience you want to be tighter to the outside. Say centered you had 1/2" on both sides, I'd move it to 1/4" outside and 3/4" inside. Under hard cornering outside tire moves away from fender and towards inner tub and spring. The other side is moving toward the fender a little but its also traveling away to. Plus tires dont flex near as much at the tops. Ontop of that with 18's 35-40 series rubber, sidewalls flex in minimal.