Wheel and Tire Fitment Comparator
Compare where two setups sit in the wheel well. Use the calculator below. Results update as you type.
How the Wheel and Tire Fitment Comparator Works
This comparator works by comparing a full current setup (tire, wheel width and offset) with a full proposed setup. It reports diameter change, inner edge change and outer edge change together.
- Enter the current tire and wheel, for example 245/40R18 on 8.0 in ET45.
- Enter the proposed tire and wheel, for example 255/35R19 on 8.5 in ET35.
- Read the diameter change: +0.31 in.
- Read the edge moves: inner −3.7 mm, outer +16.4 mm.
The Formula
The formula combines the diameter, inner edge and outer edge equations in one result.
Diameter Change = D_new − D_old Inner Edge (mm) = (W_new − W_old) × 12.7 + (ET_new − ET_old) Outer Edge (mm) = (W_new − W_old) × 12.7 − (ET_new − ET_old)12.7 is half of 25.4: each inch of wheel width splits evenly to each side. Worked example: 7.5 in ET44 to 8.5 in ET0 gives inner 12.7 − 44 = −31.3 mm and outer 12.7 + 44 = +56.7 mm.
Conversion Table
The conversion table compares 4 complete setups. Each row shows the diameter change in inches and the inner and outer edge moves in millimeters.
The truck setup (265/70R17 on ET44 to 285/70R17 on ET0) pushes the outer edge 56.7 mm (2.23 in). That is a common "aggressive offset" truck build.
| Current | Proposed | Diameter (in) | Inner Edge | Outer Edge |
|---|---|---|---|---|
| 225/45R17 on 7.5x ET45 | 235/40R18 on 8.0x ET40 | +0.43 | +1.3 | +11.3 |
| 245/40R18 on 8.0x ET45 | 255/35R19 on 8.5x ET35 | +0.31 | -3.7 | +16.4 |
| 265/70R17 on 7.5x ET44 | 285/70R17 on 8.5x ET0 | +1.10 | -31.3 | +56.7 |
| 275/60R20 on 8.5x ET44 | 295/60R20 on 9.0x ET18 | +0.94 | -19.6 | +32.4 |
What Is the Wheel and Tire Fitment Comparator?
The Wheel and Tire Fitment Comparator is a tool that compares two complete wheel-and-tire packages in one view. Most fitment problems come from combining a tire change with a wheel change, and this tool covers both.
The comparator answers 3 questions at once: will it be taller, will it hit the strut, and will it stick out past the fender?
Common Uses
This comparator has 4 uses: package shopping, build planning, swap checks and forum comparisons.
- Shop for packages: Compare dealer wheel-and-tire packages.
- Plan builds: Test full setups before buying.
- Check swaps: Compare OEM wheels from other trims.
- Compare forum setups: Translate other owners' fitments.