Offset Difference Calculator
See how a new offset moves the wheel. Use the calculator below. Results update as you type.
Offset = Distance from Wheel Centerline to Hub Mounting FaceHow the Offset Difference Calculator Works
This calculator works by subtracting the current offset from the proposed offset to show how far the wheel moves in or out. It applies to wheels of the same width.
- Enter the current offset, for example ET45.
- Enter the proposed offset, for example ET35.
- Read the offset change: −10 mm.
- Read the movement: the outer edge moves 10 mm (0.39 in) out, and the inner edge moves 10 mm away from the strut.
The Formula
The formula is Offset Change = Proposed Offset − Current Offset. The outer edge moves by the negative of that change.
Offset = Distance from Wheel Centerline to Hub Mounting Face Offset Change = ET_new − ET_old Outer Edge Move = −Offset Change Inner Edge Move = +Offset ChangeWorked example: ET44 to ET18 is −26 mm. The outer edge moves 26 mm (1.02 in) outward.
Conversion Table
The conversion table shows the offset change and edge movement for 10 offset swaps on wheels of the same width. Changes run from −26 mm to +15 mm.
The note under the table states the sign rule for both edges.
| Current | Proposed | Offset Change | Outer Edge Move | Inner Edge Move |
|---|---|---|---|---|
| ET45 | ET40 | -5 | +5 | -5 |
| ET45 | ET35 | -10 | +10 | -10 |
| ET45 | ET30 | -15 | +15 | -15 |
| ET40 | ET20 | -20 | +20 | -20 |
| ET35 | ET15 | -20 | +20 | -20 |
| ET44 | ET18 | -26 | +26 | -26 |
| ET18 | ET0 | -18 | +18 | -18 |
| ET0 | ET-12 | -12 | +12 | -12 |
| ET35 | ET50 | +15 | -15 | +15 |
| ET25 | ET40 | +15 | -15 | +15 |
Outer edge: + means more poke toward the fender. Inner edge: + means closer to the strut, − means away from it.
What Is the Offset Difference Calculator?
The Offset Difference Calculator is a tool that measures how an offset change moves a wheel in or out. It isolates offset from width changes.
A lower offset number pushes the wheel outward. A higher offset number pulls it inward. Each millimeter of offset change moves both edges by 1 mm in the same direction.
Common Uses
This calculator has 4 uses: stance changes, clearance fixes, OEM swaps and spacer comparisons.
- Change stance: Push wheels flush with the fender.
- Fix clearance: Pull wheels in away from fenders.
- Swap OEM wheels: Compare offsets across models.
- Compare spacers: Weigh a spacer against a new wheel.