Outer Wheel Position Calculator
Estimate how far a new wheel's outer edge moves toward the fender. Compare frontspacing of two wheels from width and offset.
Estimate changes at the outer wheel edge.
Outer Wheel Position Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Outer Wheel Position Calculator Works?
The Outer Wheel Position Calculator works by calculating the frontspacing of both wheels and subtracting the old value from the new value. A positive result moves the outer edge outward. The tool uses 3 steps.
Enter the current wheel
Type the width and offset, for example 8.0 in ET+18.
Enter the new wheel
Type the new width and offset, for example 10.0 in ET−25.
Read the change
The calculator returns a 68.4 mm (2.69 in) outward movement of the outer rim edge.
Outer Wheel Position Calculator Formula
The Outer Wheel Position Calculator formula is Δouter = FS_new − FS_old = (W_new − W_old) × 12.7 − (ET_new − ET_old).
FS = (W + 1) × 12.7 − ETΔout = FS_new − FS_old- FS
- Frontspacing (mm)
- W
- Nominal width (in)
- ET
- Offset (mm)
Worked example
An 8.0 in ET+18 wheel has 96.3 mm of frontspacing. A 10.0 in ET−25 wheel has 164.7 mm. The outer edge moves 68.4 mm (2.69 in) outward.
Outer Wheel Position Calculator Conversion Table
The Outer Wheel Position Calculator conversion table shows outer rim edge movement for 6 wheel changes.
| Wheel change | Old frontspacing | New frontspacing | Outer edge change |
|---|---|---|---|
| 7.5" ET+45 → 8.5" ET+45 | 62.9 mm | 75.6 mm | +12.7 mm (+0.50 in) |
| 7.5" ET+45 → 8.5" ET+35 | 62.9 mm | 85.6 mm | +22.7 mm (+0.89 in) |
| 8.0" ET+35 → 9.0" ET+35 | 79.3 mm | 92.0 mm | +12.7 mm (+0.50 in) |
| 8.0" ET+35 → 9.0" ET+20 | 79.3 mm | 107.0 mm | +27.7 mm (+1.09 in) |
| 8.0" ET+18 → 9.0" ET+0 | 96.3 mm | 127.0 mm | +30.7 mm (+1.21 in) |
| 8.0" ET+18 → 10.0" ET-25 | 96.3 mm | 164.7 mm | +68.4 mm (+2.69 in) |
What is Outer Wheel Position Calculator?
An Outer Wheel Position Calculator is a tool that predicts how far a new wheel's outer face moves relative to the old wheel. The outer face position decides whether the wheel sits tucked, flush or poking past the fender.
Lower offset and wider wheels both move the outer edge outward. The 2 effects stack.
The calculator measures the rim edge. Tire sidewall bulge usually extends a few millimeters past the rim edge.
What are the uses of Outer Wheel Position Calculator?
There are 4 main uses of the Outer Wheel Position Calculator, including stance planning and fender protection.
Stance planning
Pick a wheel spec that lands flush with the fender.
Fender protection
Avoid rim contact with the fender on compression.
Off-road flares
Size flares to cover deep-dish wheels.
Inspection compliance
Keep wheels inside the body where required.
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Estimate tire movement toward the fender.
Estimate changes at the inner wheel edge.