Wheel Offset Calculator
Calculate wheel offset (ET), backspacing, and centerline position.
Understand how offset affects wheel fitment and stance.
Wheel offset (marked ET from the German “Einpresstiefe,” meaning insertion depth) defines where the wheel’s mounting face sits relative to the centerline of the rim. It is measured in millimeters and is critical for wheel fitment, suspension geometry, bearing load, and overall vehicle stance.
The three types of offset:
- Positive offset (ET+) — The mounting face is outboard of the wheel centerline. Most front-wheel-drive cars and modern vehicles use positive offset. The wheel sits inboard (tucked in under the fender).
- Zero offset (ET0) — The mounting face is exactly at the wheel centerline.
- Negative offset (ET−) — The mounting face is inboard of the wheel centerline. The wheel sticks outward (aggressive “deep dish” stance). Common on trucks and off-road vehicles.
Key formulas:
Centerline Position = Wheel Width ÷ 2
Offset (ET) = Mounting Face Distance from Inboard Edge − Centerline Position
Backspacing = (Wheel Width / 2) + Offset + Mounting Flange Thickness
Where wheel width and offset are in the same units (mm is standard).
Example:
- Wheel width: 8 inches (203 mm)
- Centerline = 203 / 2 = 101.5 mm
- If the mounting face is 116.5 mm from the inboard edge:
- Offset = 116.5 − 101.5 = ET+15
Effect on fitment and handling:
- Higher positive offset → wheel sits more inboard → less track width → may rub on suspension components
- Lower / more negative offset → wheel sits more outboard → wider track → more understeer resistance, but may rub on fender
- Changing offset by more than ±10mm from OEM can affect bearing load, steering feel, and speedometer accuracy
Common OEM offset ranges:
- Compact FWD cars: ET+35 to ET+50
- SUVs and pickups: ET+10 to ET+30
- Sports RWD cars: ET+20 to ET+40
- Off-road trucks (lifted): ET0 to ET−25
Metric note: Offset is always measured in millimeters (mm), even on vehicles that otherwise use imperial dimensions.