Wheel Backspacing Calculator
Calculate wheel backspacing from wheel width and offset. Get the distance from hub face to inner rim edge in mm and inches.
Calculate backspacing using specified wheel dimensions.
Wheel Backspacing Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Wheel Backspacing Calculator Works?
The Wheel Backspacing Calculator works by adding the offset to half of the wheel's overall width. The tool uses 3 steps.
Enter wheel width
Type the nominal width, for example 9.0 in.
Enter offset
Type the offset, for example ET+18.
Read backspacing
The calculator adds 18 mm to half of the 10 in (254 mm) overall width and returns 145 mm (5.71 in).
Wheel Backspacing Calculator Formula
The Wheel Backspacing Calculator formula is BS = (W_nom + 1) × 25.4 ÷ 2 + ET.
BS = (W_nom + 1) × 12.7 + ETBS_in = (W_nom + 1) ÷ 2 + ET ÷ 25.4- W_nom
- Nominal wheel width (in)
- ET
- Offset (mm)
- BS
- Hub face to inner flange (mm)
Worked example
A 12.0 in wheel at ET−44 has an overall width of 13 in (330.2 mm). Backspacing is 165.1 − 44 = 121.1 mm (4.77 in).
Wheel Backspacing Calculator Conversion Table
The Wheel Backspacing Calculator conversion table lists backspacing for 8 common passenger and truck wheel specs.
| Wheel width | Offset | Backspacing (mm) | Backspacing (in) |
|---|---|---|---|
| 7.0" | ET+40 | 141.6 mm | 5.57 in |
| 7.5" | ET+45 | 152.9 mm | 6.02 in |
| 8.0" | ET+35 | 149.3 mm | 5.88 in |
| 8.5" | ET+30 | 150.6 mm | 5.93 in |
| 9.0" | ET+18 | 145.0 mm | 5.71 in |
| 9.0" | ET+0 | 127.0 mm | 5.00 in |
| 10.0" | ET-25 | 114.7 mm | 4.52 in |
| 12.0" | ET-44 | 121.1 mm | 4.77 in |
What is Wheel Backspacing Calculator?
A Wheel Backspacing Calculator is a tool that finds the distance from the wheel's hub mounting face to its inner edge. Backspacing tells how much room the wheel takes up toward the suspension.
Truck and off-road wheel catalogs often list backspacing in inches. Car wheel catalogs list offset in mm. The calculator converts between the 2 conventions.
Lower backspacing moves the wheel outward and frees room at the inner edge.
What are the uses of Wheel Backspacing Calculator?
There are 4 main uses of the Wheel Backspacing Calculator, including suspension clearance and catalog conversion.
Suspension clearance
Compare backspacing with the measured room to the control arm.
Catalog conversion
Turn an ET listing into a backspacing value.
Lift kit specs
Match the maximum backspacing a lift kit maker allows.
Steering lock checks
Check inner room for full-lock turns.
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