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How Important are Offset and Backspacing?

Offset And Backspacing Diagram
Ken Brubaker
| Senior Editor, Four Wheeler
Posted February 1, 2011

A Perfect Fit

Sometimes, conversations about wheel offset and backspacing can induce glazed eyes and distant stares. Some folks would rather be forced to write a thesis on particle physics with a crayon in a regional turboprop aircraft lavatory. But the reality is that offset and backspacing really aren't that deep, and as a bonus, wheel manufacturers and suspension companies have done the majority of the work for you.

Backspacing is the distance from the rear of the wheel hub mounting surface to the outer edge of the inboard side of the wheel. Backspacing is typically measured in inches. Offset, measured in millimeters, tells you where the hub mounting surface of the wheel is located relative to the overall width of the wheel. It is the distance from the exact center of the wheel to the outer edges of the wheel. If the hub mounting surface is centered in the wheel, the offset is zero. If the hub mounting surface is inboard of the wheel's center, the offset is negative and the wheel will be pushed out from the vehicle. If the hub mounting surface is outboard of the wheels center, the offset is positive and the wheel will tuck in on the vehicle. The illustration pictured above shows this.

Your stock rig rolled off the assembly line with a set of wheels specifically designed by the manufacturer to allow for adequate clearance between the wheel and tire and things like brake calipers, tie-rod ends, and fenders. Most factory wheels are designed with a positive offset, which result in the tire and wheel being tucked in close to the vehicle.

When you lift your rig and install a larger tire, you obviously change things from how they were designed at the factory. Naturally, it is unacceptable for the tire and wheel to contact anything on your rig during steering maneuvers and as the suspension articulates. In most cases, you'll need to install a wheel that has a negative offset. This will move the wheel outward on the vehicle and help create room for the wider, larger tire. How do you know what to install? Well, the reality is that suspension companies do the work for you. All aftermarket suspension companies provide information on what tire and wheel combination is recommended for a given kit on a specific vehicle. Naturally, it's wise to abide by that information, as it's derived from a significant amount of research and testing.

When you install the recommended wheel, you'll not only ensure that the wheel and tire will travel freely, you'll probably also increase your vehicle's track width, which improves stability. The downside is that you may see an increased sensitivity to tracking, which may require higher steering effort. It may also contribute to an increased turning radius and create more leverage on the wheel lugs, bearings, spindles and axlehousing. This increase in width may also cause the wheel/tire combo to protrude past the fender, which is illegal in some states, requiring the installation of fender flares.

If you just want to install a cool set of wheels without a suspension lift, or if you've only added a leveling kit, and you don't want to install a wheel that protrudes from your fenders, there are wheel options available. One is the Torque wheel from Dick Cepek. This wheel has a positive offset so it tucks the wheel and tire close to the vehicle. Don Sneddon, advertising manager at Mickey Thompson Tires, says, "The whole reason we came out with the Torque was to fit vehicles with no lift kit or with a leveling kit so that the wheels are very close to a factory offset."

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