Wheel 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 between the hub mounting surface and the back end of the wheel. Backspacing is especially important to factor in when the new wheel and tire package is wider than what came on the vehicle. It is crucial to ensure that the new package has enough clearance so that nothing rubs against the suspension, brakes, or vehicle body, like fenders, bumpers, and mud flaps.
Wheel backspacing and wheel offset are essentially the same thing, but they use different methods and measurements (inches vs. mm) to determine how far inward or outward tires will sit on a vehicle. Proper offset assures that the new package has enough clearance so that nothing rubs against the suspension, brakes, or vehicle body. It is also important for driving safety, since the wrong offset can reduce vehicle stability or interfere with braking.
When calculating wheel backspace, measurements are determined in inches. The distance from the centerline of the wheel to the hub mounting surface is called the wheel offset. There are three types of wheel offset:
- Zero wheel offset is when the hub mounting surface is in line with the centerline of the wheel.
- Positive wheel offset is when the hub mounting surface is in front (more toward the street side) of the centerline of the wheel. Most wheels on front-wheel drive cars and newer rear-drive vehicles have positive offset.
- Negative offset is when the hub mounting surface is behind the wheel centerline. "Deep dish" wheels are typically a negative offset.
In summary, wheel backspacing is the distance from the mounting surface to the wheels back lip, while wheel offset refers to how the wheels and tires are mounted and sit in the wheel wells.
