This simple, homemade tool works best on the rear and can be used to simulate either the wheel width or the section width of the tire to establish proper clearance. The tool can be used on the front, but it's more difficult to ensure that everything will clear. The problem is simulating ride height while being able to turn the wheel to check for clearance. Try placing the floor jack directly underneath the lower ball joint and raising the jack to ride height. This is especially important because the front suspension moves in an arc inboard as it moves up into the wheelwell.