🛠️ Wheel Offset & Backspacing Calculator
Convert between wheel offset (ET) and backspacing from your wheel width — the two ways of describing where a wheel sits, so you can compare fitments.
Backspacing
5.77″
146.6 mm
Front spacing
56.6 mm
Backspacing = wheel width ÷ 2 + offset. Offset (ET) is the distance from the mounting face to the wheel’s centreline: positive pulls the wheel inward, negative pushes it out. A more positive offset (or greater backspacing) tucks the wheel further under the arch. 🔒 In your browser.
How the wheel offset & backspacing calculator works
Offset and backspacing describe the same thing two ways. Backspacing is the distance from the wheel’s mounting face to its inner lip; offset (ET) is the distance from the mounting face to the wheel’s centreline. They’re related by: backspacing = wheel width ÷ 2 + offset (converting the width to millimetres). The tool converts either way.
A more positive offset (or larger backspacing) tucks the wheel further inboard under the arch; a lower or negative offset pushes it outboard for a wider stance. Changing offset affects clearance, steering and bearing loads, so compare against your original wheels before fitting.
Frequently asked questions
What is wheel offset?
Offset (marked ET, from the German Einpresstiefe) is the distance in millimetres from the wheel’s mounting face to its centreline. Positive offset sits the face outboard of centre (wheel tucked in); negative offset pushes the wheel outward.
What is backspacing?
The distance from the wheel’s mounting face to its inner (back) lip, usually in inches. More backspacing pulls the wheel inboard. It’s related to offset by backspacing = width ÷ 2 + offset.
How do I convert offset to backspacing?
Backspacing (mm) = wheel width ÷ 2 + offset, with the width converted from inches to millimetres. For an 8″ wheel with +45 mm offset: (8 × 25.4) ÷ 2 + 45 = 101.6 + 45 = 146.6 mm ≈ 5.77″.
Does changing offset affect fitment?
Yes. A lower/negative offset moves the wheel outward (wider track, possible fender or suspension rubbing); a higher offset pulls it inward (possible strut/brake clearance issues). Stay close to the original offset unless you’ve checked clearances.
Is more offset better?
Neither is universally better — it depends on the vehicle. The safe approach is to match the manufacturer’s offset, or change it only after checking clearance to the suspension, brakes and fenders. Big changes also load wheel bearings differently.