[fourwd1]

Questions on this come up all the time. This may help answer some.

Offset

The offset of a wheel is the distance from its hub mounting surface to the centerline of the wheel. The offset can be one of three types (measured in millimeters).*

Zero Offset -
The hub mounting surface is even with the centerline of the wheel.

Positive Offset -
The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.

Negative Offset -
The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.

If the offset of the wheel is not correct for the car, the handling can be adversely affected. When the width of the wheel changes, the offset also changes numerically. If the offset were to stay the same while you added width, the additional width would be split evenly between the inside and outside. For most cars, this won't work correctly.

Backspacing

Backspacing, similar to offset, is the distance from the hub mounting surface to the inside lip of the wheel (measured in inches).

How to Measure Wheel Backspace :
Items required to measure wheel backspace:
- Tape measure
- Straight edge
- Wheel w/o tire (preferred)



The easiest way to measure backspace is to lay the wheel face down onto the ground so the backside of the wheel is facing up. Take a straight edge and lay it diagonally across the inboard flange of the wheel. Take a tape measure and measure the distance from where the straight edge contacts the inboard flange to the hub mounting pad of the wheel. This measurement is backspace.

The above diagram shows three wheels with 2",3", & 4" backspace.

Measuring Wheel Offset
To calculate offset you'll need the following measurements:
- Wheel backspace
- Wheel Width
- Wheel Center line (outboard flange to inboard flange measurement / 2)



Subtract:
Wheel center line from Wheel backspace to get offset.
- If backspace is less than the wheel centerline the offset is negative
- If backspace is greater than the wheel centerline the offset is positive

Tip:
To convert from inches to mm multiply by 25.4
To convert from mm to inches divide by 25.4

Wheel terminology