Wheel Offset Calculator
Enter your current wheel and the one you are thinking about. You will see how much closer the new wheel sits to the strut, how far it pokes out toward the fender, and the backspacing of each.
Result
| Current | New | |
|---|---|---|
| Backspacing | ||
| Front spacing | ||
| Effective offset |
What wheel offset means
Offset, stamped on the wheel as ET, is the distance in millimeters from the center line of the wheel to the face that bolts against the hub. A wheel with ET45 has its mounting face 45 mm toward the outside of the car from its center line.
- Higher offset (ET45, ET50) pulls the wheel in toward the strut.
- Lower offset (ET20, ET0) pushes the wheel out toward the fender.
- Negative offset (ET-12) puts the mounting face behind the center line, common on trucks.
How the calculator works
A wheel's overall width is its rim width plus about 1 inch for the lips on both sides. That is the usual convention for backspacing, and the one this calculator uses.
- Backspacing = half the overall width + offset. It is how far the wheel reaches in from the hub face toward the suspension.
- Front spacing = overall width − backspacing. It is how far the wheel reaches out from the hub face toward the fender.
- Inside change = new backspacing − current backspacing.
- Outside change (poke) = new front spacing − current front spacing.
Example: going from an 8 in ET45 to a 9 in ET35 moves the inside of the wheel about 3 mm closer to the strut and the outside about 23 mm further out.
Spacers
A spacer lowers the effective offset by its own thickness. A 10 mm spacer on an ET45 wheel makes it behave like an ET35. Use hub-centric spacers, and check that you still have enough thread engagement on the studs or bolts.
Offset on a lowered car
Lowering changes what fits. As the car drops, the top of the tire moves closer to the fender lip, and most cars gain negative camber, which tucks the top of the wheel in. That is why a wheel that pokes on a stock-height car can sit flush once it is lowered, and why coilovers can leave less room on the inside than the factory strut. Plan the wheel and the drop together.
Work out the drop and the tire size change with the ride height and fitment calculator, then shop coilovers, lowering springs or camber and alignment kits by car.
Wheel offset FAQ
Is a higher or lower offset better?
Neither. Higher offset tucks the wheel in, lower offset pushes it out. The right number is the one that clears your suspension on the inside and your fender on the outside.
How much poke is too much?
On a lowered car, more than about 10 mm of extra poke often needs rolled fenders or some negative camber. On a stock-height car you usually have more room at the top of the fender.
Does a wider wheel change the offset?
No, but it changes both sides. At the same offset, every extra inch of width adds about 12.7 mm on the inside and 12.7 mm on the outside.
Is backspacing the same as offset?
No. Offset is measured from the center line of the wheel. Backspacing is measured from the inner lip. Two wheels with the same offset but different widths have different backspacing.