Backspacing is a measurement system used to determine where the wheels and tires are placed when bolted onto a vehicles hub mounting surface. It is the distance from the back of the mounting pad to the back lip of the wheel. Backspacing is measured by laying the wheel on its face, placing a straight edge across the wheel, and then measuring down to the mounting face. The higher this measurement, the more the wheel is pushed inboard towards the cars centerline.

In contrast, offset is the distance from the mounting surface to the centerline of the wheel, expressed in millimeters. Positive offset means that the wheels are pushed inboard towards the centerline of the car, while negative offset means that the wheels are moved outboard towards the fenders, widening the track.

While backspacing and offset are essentially the same thing, they use different methods and measurements (inches vs. mm) to determine how far inward or outward tires will sit on a vehicle. Understanding wheel backspacing and offset can be crucial to a vehicles look, feel, and handling. When driving, it is important to ensure that the wheels and tires do not rub against essential components.