While shopping for wheels, you will no doubt come across some terms like rim width, rim size and offset (or backspacing). While the rim width or rim size may be pretty straight forward, understanding the offset or backspacing can make all the difference in getting the perfect look and feel for your new wheels. The offset measures the distance between the wheel’s mounting surface and the centerline of the wheel, while the backspacing measures the distance between the wheel’s mounting surface and the back lip of the wheel. These measurements help determine which wheels are compatible with which vehicles, so the wheels do not stick out too far past your fender or tuck too far under the fender. Every vehicle is different and getting the right offset or backspacing will make sure you get the most out of your new wheels so they not only look great, they are simply a perfect fit.
Wheel Offset and Backspacing Conversion Chart
The wheel offset describes the wheel’s ideal position, so that it can freely rotate without rubbing against the fender, brakes or any suspension components. It quickly tells you how far in or out towards the fender the wheel will be.
A wheel’s offset is determined by measuring the distance between the wheel centerline and the mounting surface on the back of the wheel. The offset is measured in millimeters, which can be positive, zero or negative.
- Positive offset - the mounting surface extends past the centerline and closer to the face of the wheel
- Zero offset - the mounting surface lines up with the centerline of the wheel
- Negative offset - the mounting surface is closer to the back of the wheel
Every vehicle requires a specific offset wheel. Most modern vehicles usually are equipped with a positive offset wheel from the factory. Some rear-wheel-drive vehicles are closer to a zero or negative offset. Most wheels have the offset embossed on the mounting surface or on a spoke on the back side of the wheel.
Check out the diagrams below for a visual illustration of each offset type. You can see how a positive offset will tuck the wheel assembly further under the fender, while a zero or negative offset pushes the wheel out towards or even past the fender.
Backspacing is an older system of measurement to determine how deep the mounting pad is located on the wheel. While offset was measured in millimeters, the backspace is measured in inches. The correct backspacing will allow enough room for the suspension, brakes and steering systems to operate without interference from the wheel. A positive offset creates more backspace, while a negative offset reduces the backspace.
The backspacing is determined by measuring the distance between the wheel’s mounting surface on the back of the wheel and the outer lip of the wheel. Like offset, each wheel’s backspacing depends on the vehicle’s size and design. To measure this distance, lay the wheel down with the back side of the wheel facing up. Be sure to lay the wheel on a soft surface so the face of the wheel is not scratched or damaged while making these measurements. Place a solid item across the wheel so that there is a flat surface touching both sides of the wheel. Use a ruler or tape measure to measure the distance from the back mounting surface of the wheel to the lowest point on the object you use.
For example, an 8 inch wide wheel with a 4.5 inch backspace would be the equivalent of a zero offset because the mounting surface aligns with the centerline of the wheel.
Our knowledgeable technicians at Discount Tire will be able to determine your vehicle’s correct offset and backspacing. Based on these measurements, we can assist you in choosing wheels that both fit your vehicle and your aesthetic preferences.
If you have any questions about offset or backspacing, stop by any of our Discount Tire locations and we'll get you taken care of!