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04.19.2013
What Is Wheel Offset and Backspacing?

wheel-offset-terms
It’s easy to confuse wheel offset and backspacing. Ironically a positive offset pulls the wheel in and a negative pushes it out. So as you can imagine the offset can influence a vehicle’s stance when combined with tire width. Offset and backspacing are important to know when choosing your wheels and tires as well as the fender flares to compliment them. Typically, a negative offset is best suited for Bushwacker Fender Flares since it will fill any additional space the flare creates.

Offset and backspacing are defined as:

Wheel Offset
Wheel offset (abbreviated ET) is the distance from the mounting surface of the hub (M) to the wheel’s centerline (C). Offset can be positive or negative and is typically measured in millimeters.

Wheel Backspacing
This is the distance created between the plane of the inner rim and the mounting surface of the hub (M).

In essence, the offset determines how far the wheel will push outwards. There are three types of offset:

wheel-offset-diagramZero Offset
The plane of the hub’s mounting surface is aligned with the centerline of the wheel. Example: the mounting surface on an 8″ wide wheel would align 4″ in from the inner and outer rim.

Positive Offset
The plane of the hub’s mounting surface is pushed toward the outside of the wheel. The wheel is drawn in which causes it to wrap around the hub and brake. Example

Negative Offset
The plane of the hub’s mounting surface is pulled toward the inside of the wheel. This pushes the wheel out which results in a wider stance. Example

As you can see, the wheel’s offset drastically affects the appearance of a truck or SUV.

Naturally, a wheel with a negative offset will look best with fender flares that have two or more inches of tire coverage.

For the Bushwacker TJ build we used Raceline Monster beadlocks, which have a good amount backspace without much offset. Out of the box they come with a -0.1″ offset which created 4.7″ of backspacing. This placed the 12.5″ wide tires perfectly with our flat flares, which offer six inches of coverage.

Be sure to talk to a wheel and tire specialist when putting together your package together. The important thing to remember is that a positive offset sucks the wheel in, and a negative pushes it out. This covers the basics of offset and backspacing, there are plenty of resources online that can provide in depth knowledge on the topic if needed. Below is one of the most handy calculators for offset and backspacing. Take note that it only accepts metric sizing for tires, but will convert into inches:

wheel-offset-backspacing-calculator