The offset of a vehicle's wheel is the distance between the centreline of the wheel and the plane of the hub-mounting surface of the wheel. It can thus be either positive or negative, and is typically measured in millimetres.
Offset has a significant effect on many elements of a vehicle's suspension, including suspension geometry, clearance between the tyre and suspension elements, the scrub radius of the steering system, and visually, the width of the wheel face relative to the car's bodywork."Deep dish" wheels typically have negative offset or a very low positive offset. Wheels are usually stamped with their offset using the German prefix "ET", meaning "Einpresstiefe" or, literally, "press depth". An example would be "ET45" for a 45mm offset.
Zero Offset
When the plane of the hub mounting surface is even with the centreline of the wheel.
Positive Offset
When the plane of the hub mounting surface is shifted from the centreline toward the front or outside of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.
Negative Offset
When the plane of the hub mounting surface is toward the back or brake side of the wheel's centreline.