Wheel Offset is the distance between a wheel’s mounting face and the centerline of its rim width, positive when the mounting face sits outboard of the centerline. It is stated in millimeters and, together with rim width, it fixes where the wheel and tire sit relative to the hub, so it determines inner clearance to the suspension and frame and outer clearance to the fender. Offset also changes track width and the scrub radius, since moving the wheel outboard shifts the tire centerline away from the steering axis and increases the leverage that braking and traction forces exert on the steering. Backspacing describes the same relationship measured from the mounting face to the inner rim flange, and the two convert into one another once rim width is known.