Wheel Offset Change Calculator

About this calculator

Wheel offset (ET) is the distance in millimetres between a wheel’s true centerline and its mounting hub face — a higher ET pulls the wheel’s face inward toward the car, a lower ET pushes it outward. When either wheel width or ET changes, the wheel’s outer edge (how far it “pokes” outward) and inner edge (how close it sits to suspension components) both shift, and the amount is half the width change plus the full offset change in each direction, applied separately to the inner and outer lip.

Car enthusiasts fitting wider wheels or a different offset run this calculation before buying, because getting it wrong means either the wheel rubs the fender at the outer edge or fouls suspension and brake components at the inner edge — problems that only become obvious once the wheel is mounted and the car is back on the ground, by which point a return or refit is expensive and inconvenient.

This calculator takes your old and new wheel width and ET offset, and returns exactly how many millimetres the outer and inner edges of the wheel move, so you can check fender and suspension clearance before you buy.