Offset Wheel Calculator

The marked width stamped on the wheel, measured between bead seats.
Positive offset moves the mounting face outboard and the wheel inboard.
Optional. Gap between the current inner rim edge and the strut or suspension, so the calculator can show what is left.
Optional. Gap between the current outer rim edge and the fender lip.
Inner rim edge moves inward by
12.70 mm
Wheel Offset and Backspacing Calculator
Outer rim edge moves outward by
12.70 mm
Inner edge
12.7 mm further in toward the suspension
Outer edge
12.7 mm further out past the fender line
Offset change
0.00 mm
Width change
1.000 in
Width change
25.40 mm
Current backspacing
5.575 in
New backspacing
6.075 in
Backspacing change
0.500 in
Wheel centreline moves outward by
-0.00 mm
Track width change (both wheels)
-0.00 mm
Worked out from NIST Guide to the SI, Appendix B.9 conversion factors and 2 other sources.
This is a geometric estimate of rim-edge movement only. It does not certify tire, brake, suspension, fender, hub or bolt-pattern clearance, or load rating. Check physical clearance at full lock and full suspension travel before fitting wheels.

How this is worked out

5 steps
  1. Width term = (8 - 7) x 25.4 / 2 = 12.7 mm added to each rim edge.
  2. Offset change = 40 - 40 = 0 mm; a positive change pulls the whole wheel inboard.
  3. Inner edge change = 12.7 + 0 = 12.7 mm (positive = toward the suspension).
  4. Outer edge change = 12.7 - 0 = 12.7 mm (positive = further out past the fender).
  5. Backspacing goes from 7/2 + 1.575 + 0.5 = 5.575 in to 6.075 in.

Results are general information, not financial, tax, legal, medical or engineering advice.