The offset of a wheel is the measurement from a wheels imaginary centre line to the mounting face, and is commonly shown as ET. For most modern vehicles the offset will be positive, which means the mounting face is forward of the centre line, bringing the wheel further under the bodywork of the car. Older cars and some 4×4 vehicles will have negative offset, which pushes the wheel outwards from the car’s bodywork. Aftermarket wheels may have a lower offset than the vehicles standard wheels and this is to accommodate the fact that the aftermarket wheel is invariably wider than the vehicles standard wheels. It must be stressed that too great an offset reduction will affect the car’s stability and roadholding and will cause accelerated wear to drive-train and suspension components.
Zero Offset – The plane of the hub mounting surface is even with the centerline of the wheel.
Positive Offset – The plane of the hub mounting surface is shifted from the centerline toward the front or face of the wheel.
Negative Offset – The plane of the hub mounting surface is toward the back or brake side of the wheel’s centerline.