Backspacing and offset are often confused, but are not the same. Some wheels will have offset molded or stamped into them. If the wheels you’re looking at do not offer that information, this diagram of a wheel cross section shows how the two measurements are derived. Offset is the backspacing minus the centerline. The centerline is one-half of the overall outside width of the wheel. If the centerline is greater than the backspacing, it’s a negative offset; less than the backspacing, it’s a positive offset.