WHEEL AND TIRE TECH 101
Get a better understanding of the wheels on your car
Offset is the location of the flat mounting surface of a wheel relative to the wheel’s centerline. Negative offset means that the mounting surface is toward the center of the car, positive offset means that it’s toward the outside of the car, or the wheel is “pulled in” toward the center. Offset affects many things other than just whether the wheel has the appearance of “sticking out” past the fender. The wrong offset can cause rubbing problems when the suspension is compressed or the wheel is turned. Offset affects the steering ge- ometry’s scrub radius, possibly leading to problems with torque steer or self-centering characteristics.
Offset also affects the suspension’s motion ratio, which directly determines the effective spring and damper rates. Potentially, in a very heavily loaded vehicle, or with extreme changes in offsets, wheel bearing life can be affected, but this is more often talked about by truck people than by small car enthusiasts. It’s very, very important that the proper offset wheels be used.
While not directly a matter of offset, brake caliper clearance is a related issue. If you have or plan to have big brakes on your car, be sure that your wheels, or the wheels that you’re going to use will fit over the calipers. Spacers are available to solve the problem if they don’t, but it’s best to get a wheel with enough dish to meet your offset specs and still fit your brakes. Consulting the wheel and brake manufacturers ahead of time is wise. Many aftermarket brake companies even have templates of their brakes available that you can easily check against any wheel.
NEGATIVE OFFSETZERO OFFSETPOSITIVE OFFSET