Wheel Tools
Offset, wheel position and backspacing.
Methodology & limits
Know where your wheel moves.
Width and offset work together. Measure how a new wheel moves toward the suspension or the fender, and convert backspacing with the right reference dimensions.
Nominal wheel width is measured between rim reference planes. It does not include the full physical width of both lips. Read the methodology and limits.
What wheel offset means
Offset, often marked ET, is the signed distance in millimeters between the wheel centerline and its mounting face. With the same wheel width, increasing positive offset moves the wheel inward.
A wheel marked 18x8 ET35 has a nominal width of 203.2 mm. Its nominal inner reach is 136.6 mm and its outer reach is 66.6 mm, both measured from the mounting face.
Offset and backspacing use different references
Backspacing reaches to the inner physical lip. To calculate it, supply the overall wheel width with an explicit symmetry assumption, or the extension of the inner flange beyond the nominal rim plane. The calculator never adds a hidden inch to the width.
Choose a tool
Use Wheel Offset Calculator for one wheel, Wheel Offset Comparison for a change, and Backspacing Calculator to convert a physical measurement.