Wheel Offset Calculator
Estimate wheel offset from measured overall width and backspacing. A positive result locates the mounting face outward from the centreline.
How the result changes
Only overall wheel width changes; all other inputs stay at your current values. The line illustrates the formula across the shown range. This is not a forecast of real-world outcomes.
About this calculation
Wheel offset describes where the mounting face sits relative to the wheel's centreline. When overall width and backspacing are both physically measured in millimetres, their difference gives a signed offset. Calculate wheel offset when planning a trip or vehicle expense.
Formula
offset = backspacing − half of measured overall wheel width
Worked example
With Overall wheel width: 220 mm, Backspacing: 130 mm, offset is 20 mm.
Inputs and units
Measure overall width from the outer edge of one flange to the outer edge of the other. Backspacing is the depth from the mounting face toward the vehicle-side edge; use the same millimetre scale for both.
- Overall wheel width (mm): Measure outside edge to outside edge, including both flanges.
- Backspacing (mm): Measure from the wheel's inner mounting face to its innermost edge.
Calculation and worked example
Half the overall width is the distance from either outer edge to the centreline. Subtract that half-width from backspacing: a positive result puts the mounting face toward the outside edge, while a negative result puts it inward In compact notation, offset = backspacing − half of measured overall wheel width.
A wheel measuring 220 mm overall and 130 mm backspacing has a centreline at 110 mm. Its offset is 130 − 110 = +20 mm under the stated measuring convention.
How to use the answer
The signed offset is a geometry measure, not a fitment guarantee. Tyre width, brake package, suspension clearance, hub bore, and load requirements still determine whether a wheel can be used on a vehicle.
Compare a measured wheel with a replacement whose offset specification is known. Record the exact flange-to-flange width and backspacing technique; measurements taken from nominal advertised rim width do not match this formula directly.
Assumptions and checks
The wheel is symmetrical about its centreline and overall width is measured at the same flange edges used for backspacing. The mounting face is flat and the measurement does not include a spacer.
Nominal rim width often excludes flange thickness, so substituting a nominal 8-inch width for measured overall width can shift the derived offset. Also keep the sign: +20 mm and −20 mm locate the mounting face on opposite sides of centreline.
If backspacing equals exactly half overall width, offset must be zero. Increasing backspacing by 10 mm while holding width fixed should increase offset by 10 mm.
Common questions
What does the offset result represent?
It is the signed millimetre distance from wheel centreline to its mounting face using the measured overall-width convention.
What should I check before relying on this result?
Check measurement edges, sign convention, and whether a quoted wheel width is nominal or overall. Confirm actual vehicle clearance separately.
Inputs
- Overall wheel width (mm)
- Backspacing (mm)