How to Change a Wheel Offsetby Don Bowman
Wheel offset is used to move the tire either in or out from under the vehicle. In many cases, a larger rear tire can be accommodated under the body by adjusting the wheel offset. Caution must be used and the vehicle inspected well for clearance from all obstructions. Take into consideration the brake assembly for clearance and the movement of the rear axle in its vertical swing so that the tire does not hit the fenderwell. The fenderwell curves down--usually on the outside--and when a large bump is encountered that compresses the shocks, the tire may hit it.
Raise and support the vehicle on jack stands. Place the floor jack under the rear axle and raise the axle to the point that the weight is just beginning to be removed from the stands. Inspect the wheel housing for any possible problems when the axle is raised further due to road conditions. Measure the distance the tire can be moved in without hitting anything.
Remove the wheel and remove the tire from the wheel. Lay the wheel on the floor face up. Measure the distance from the floor to the bottom of the center of the wheel. Add the distance the tire is to be moved in to this measurement. This is the new offset.
Raise and support the front of the vehicle if the front wheel offset is to be changed. Raise the lower control arm with the jack until it begins to remove the weight of the car from the jack stands. Turn the steering wheel both ways and measure the clearance at the locations that come the closest to hitting. Repeat Step 2 to find the offset for the front wheels.
Purchase new wheels with the offset you came up with in Step 2. Mount the tires on the new wheels. Put the wheels on the vehicle. Double-check all clearances.