Wheel fitment
How wheel offset works
Offset locates the mounting face relative to the wheel centreline. It determines where a wheel sits before tire shape is considered.
Understand positive and negative offset
Positive offset places the mounting face toward the wheel’s outer side, moving the wheel body inward compared with zero offset at the same width. Reducing positive offset moves the wheel outward. Width changes can alter both inner and outer positions simultaneously.
Work through width and offset together
A change from 7 inches ET45 to 8 inches ET35 adds 25.4 mm of width, or 12.7 mm per side. Reducing offset by 10 mm shifts the assembly outward. The net result is 2.7 mm less inner clearance and 22.7 mm more outer protrusion.
Measure the things the formula cannot see
The calculator uses nominal bead-seat width. Wheel flange shape, spoke-to-brake clearance, tire bulge and suspension travel need physical or manufacturer checks. An acceptable outer appearance does not establish that the inner barrel or spokes clear the brakes.
Method and references
Examples use nominal geometry and fixed-price scenarios, with no vehicle-specific specifications implied. See our calculation methodology and editorial policy.
Dimension reference: Tire Rack: calculating tire dimensions. Consult the tire and vehicle manufacturers for actual fitment requirements.