What is wheel offset (ET)?
Wheel offset (ET) is the distance in millimeters from the wheel's mounting face to its centerline. Positive ET moves the wheel inward. Negative ET moves it outward. ET is the global standard measurement used by European, Asian, and most international wheel manufacturers.
ET is stamped on the back barrel of nearly every aftermarket wheel. A measurement of ET45 means the mounting face sits 45mm in front of the wheel's centerline. You can find your stock ET stamped on your current wheel or listed in your vehicle's owner's manual.
What is wheel backspacing?
Backspacing is the distance in inches from the wheel's mounting face to the inner lip of the wheel. It measures how far the wheel sits inside the fender well. Higher backspacing moves the wheel inward. Lower backspacing moves the wheel outward toward the fender.
Backspacing is most commonly used in the North American truck and off-road market. When you buy wheels from American manufacturers particularly for trucks, Jeeps, and 4x4s the fitment spec is often listed as backspacing in inches rather than ET in millimeters. An 8-inch wide wheel with 5.5 inches of backspacing positions the mounting face 5.5 inches from the inner lip.
What is the key difference between offset and backspacing?
Offset (ET) is measured from the mounting face to the wheel centerline in millimeters. Backspacing is measured from the mounting face to the inner wheel lip in inches. Offset uses the centerline as its zero point. Backspacing uses the inner edge. Both measure the same wheel from different starting points.
Wheel Offset (ET)
- Measured in millimeters
- Reference point: wheel centerline
- Can be positive, zero, or negative
- Global standard used worldwide
- Stamped on wheel back barrel
- Used by European & Asian brands
Backspacing
- Measured in inches
- Reference point: inner wheel lip
- Always a positive number
- Primarily North American market
- Listed on spec sheets, not stamped
- Used by American truck brands
How do I convert backspacing to wheel offset?
To convert backspacing to ET: multiply backspacing in inches by 25.4 to get mm, then subtract half the wheel width in mm. The formula is ET = (Backspacing × 25.4) − (Width × 25.4 ÷ 2). A 5.5-inch backspacing on an 8-inch wide wheel equals ET38.
How do I convert wheel offset to backspacing?
To convert ET to backspacing: add half the wheel width in mm to the ET value, then divide by 25.4 to convert to inches. Formula: Backspacing (inches) = (ET + Width mm ÷ 2) ÷ 25.4. An ET45 on a 7.5-inch wide wheel equals 5.54 inches of backspacing.
Which measurement should I use offset or backspacing?
Use ET if you are buying wheels from European, Asian, or international brands ET is stamped on the wheel and listed in fitment databases. Use backspacing if you are fitting wheels on an American truck or Jeep where the spec sheet lists inches. Both measure the same thing from different starting points.
| Situation | Use This Measurement | Why |
|---|
| Buying aftermarket wheels (JDM/Euro) | ET (offset) | Stamped on wheel, listed in databases |
| Fitting a truck or Jeep | Backspacing (inches) | American brands list backspacing on spec sheets |
| Cross-referencing two wheel brands | Both convert as needed | Ensures consistent comparison |
| Measuring a wheel you own | ET (offset) | Easier to measure to centerline than inner lip |
Does a higher backspacing mean more or less poke?
Higher backspacing means the wheel sits further inward less poke, more tuck. Lower backspacing means the wheel sits further outward more poke. This is the opposite of ET: higher ET = more tuck (same as higher backspacing). Lower ET = more poke (same as lower backspacing).
Both measurements move in the same physical direction they just count from opposite reference points. When you increase backspacing, the wheel moves inward, the same as increasing ET. Use our wheel offset calculator to see the poke or tuck result for any ET change without needing to convert manually.
