Wheel Backspacing

Backspacing is the distance from the inside edge of the wheel to the mounting pad of the wheel, which is where the pad seats up against the hub.

Wheel Offset

A wheel's offset is measured in a similar way but is the distance from the centerline of the wheel to where the wheel pad mounts against the hub.

Determining Backspacing

To measure backspacing, place the wheel face down. Lay a flat edge across the wheel. Use a tape measure or a ruler to measure the distance from the where the wheel mounts against the hub to the top (inner) edge of the wheel. This is the wheel's backspace.

How Does it Affect Fitment

A wheel with a smaller backspacing will be located further away from the body than a wheel with a larger backspacing. If the wheel sticks out too far (not enough backspace), it may rub the fender lip. If there is too much backspacing, it may interfere with the brakes and suspension.

Other Considerations

Incorrect backspacing can cause excessive wear on the hub and bearing and cause premature failure of these components, particularly if the wheel sticks too far out from the hub because of a lack of backspacing.

Source:

Wheel Offset vs. Backspacing

Backspacing Info.

Resource:

The Tire Rack