Inner Wheel Position Calculator
See how the inner rim edge moves. Use the calculator below. Results update as you type.
How the Inner Wheel Position Calculator Works
This calculator works by adding the wheel half-width to the offset to find the distance from the hub face to the inner bead seat. It shows exactly where the inner rim edge sits.
- Enter the wheel width, for example 8.5 in.
- Enter the offset, for example ET40.
- Read the inner position: 147.9 mm (5.82 in) from the hub face.
- Compare with a second wheel to see the change.
The Formula
The formula is Inner Position = (Width × 25.4 ÷ 2) + Offset.
Inner Position (mm) = Width (in) × 12.7 + ET (mm) Inner Change (mm) = Inner_new − Inner_oldWorked example: a 9.5 in wheel at ET30 has 120.65 + 30 = 150.6 mm to the inner bead seat.
Conversion Table
The conversion table gives the inner bead seat distance for 7 widths and 5 offsets. Distances run from 108.9 mm (7.0 in at ET20) to 172.0 mm (10.0 in at ET45).
Each 0.5 in width step adds 6.35 mm. Each 5 mm offset step adds 5 mm.
| Width (in) | ET20 | ET30 | ET35 | ET40 | ET45 |
|---|---|---|---|---|---|
| 7.0 | 108.9 | 118.9 | 123.9 | 128.9 | 133.9 |
| 7.5 | 115.2 | 125.2 | 130.2 | 135.2 | 140.2 |
| 8.0 | 121.6 | 131.6 | 136.6 | 141.6 | 146.6 |
| 8.5 | 127.9 | 137.9 | 142.9 | 147.9 | 152.9 |
| 9.0 | 134.3 | 144.3 | 149.3 | 154.3 | 159.3 |
| 9.5 | 140.6 | 150.6 | 155.6 | 160.6 | 165.6 |
| 10.0 | 147.0 | 157.0 | 162.0 | 167.0 | 172.0 |
What Is the Inner Wheel Position Calculator?
The Inner Wheel Position Calculator is a tool that finds where the inner edge of a wheel sits relative to the hub mounting face. It gives an absolute position, not just a change.
An absolute value lets you compare any wheel with a measured distance to the strut or control arm.
Common Uses
This calculator has 4 uses: strut gap checks, coilover fitment, brake-line checks and wheel comparisons.
- Check strut gaps: Compare the inner position with measured space.
- Fit coilovers: Check clearance to spring perches.
- Check brake lines: Confirm space at the hose bracket.
- Compare wheels: Rank wheels by inward reach.