Combined Wheel and Tire Comparator
Compare complete wheel and tire setups by diameter, widths, offset and backspacing. See inner and outer edge movement in one table.
Compare dimensions, widths, and offsets.
Combined Wheel and Tire Comparator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Combined Wheel and Tire Comparator Works?
The Combined Wheel and Tire Comparator works by calculating tire dimensions and wheel mounting dimensions for 2 complete setups and reporting the net movement at every edge. The tool uses 4 steps.
Enter setup A
Type the tire size and the wheel width, diameter and offset, for example 225/45 R17 on 17x7.5 ET45.
Enter setup B
Type the new tire and wheel, for example 245/40 R18 on 18x8.5 ET40.
Compute both setups
The comparator calculates diameter, backspacing, frontspacing and tire edge positions.
Read net changes
The comparator lists the change in height, inner edge and outer edge in mm and inches.
Combined Wheel and Tire Comparator Formula
The Combined Wheel and Tire Comparator formula set is Δinner = ΔW_tire ÷ 2 + ΔET and Δouter = ΔW_tire ÷ 2 − ΔET, with diameter from the size code.
BS = (W_wheel + 1) × 25.4 ÷ 2 + ETFS = (W_wheel + 1) × 25.4 ÷ 2 − ETΔin = ΔW_tire ÷ 2 + ΔETΔout = ΔW_tire ÷ 2 − ΔET- W_wheel
- Nominal wheel width (in)
- +1
- Allowance for the 2 rim flanges (about 0.5 in each)
- ET
- Offset (mm)
Worked example
Moving from 225/45 R17 on 17x7.5 ET45 to 245/40 R18 on 18x8.5 ET40 adds 18.9 mm (0.74 in) of height. The tire's inner edge moves 5 mm (0.20 in) inward, and the outer edge moves 15 mm (0.59 in) outward.
Combined Wheel and Tire Comparator Conversion Table
The Combined Wheel and Tire Comparator conversion table compares 8 measurements for a stock 17-inch setup and an 18-inch upgrade.
| Measurement | Setup A | Setup B | Change |
|---|---|---|---|
| Tire size | 225/45 R17 | 245/40 R18 | — |
| Overall diameter | 634.3 mm (24.97 in) | 653.2 mm (25.72 in) | +18.9 mm (+2.98%) |
| Section width | 225 mm (8.86 in) | 245 mm (9.65 in) | +20 mm |
| Wheel size | 17x7.5 ET45 | 18x8.5 ET40 | +1 in dia, +1 in width |
| Backspacing | 152.9 mm | 160.6 mm | +7.7 mm |
| Frontspacing | 62.9 mm | 80.6 mm | +17.7 mm |
| Inner tire edge | — | — | +5.0 mm (inward) |
| Outer tire edge | — | — | +15.0 mm (outward) |
What is Combined Wheel and Tire Comparator?
A Combined Wheel and Tire Comparator is a tool that compares 2 complete wheel-and-tire packages instead of tires alone. A wheel upgrade changes tire size, wheel width and offset together, and each change moves the tire in a different direction.
The comparator nets the 3 effects into 2 numbers: inner edge movement and outer edge movement. Those 2 numbers decide whether the package fits.
The comparator uses nominal tire width. A tire on a wider rim grows by about 5 mm (0.2 in) per 0.5 in of rim width.
What are the uses of Combined Wheel and Tire Comparator?
There are 4 main uses of the Combined Wheel and Tire Comparator, including aftermarket package checks and OE trim swaps.
Aftermarket package checks
Confirm a wheel retailer's package fits before ordering.
OE trim swaps
Compare wheels from different trims of the same model.
Winter package checks
Compare winter and summer packages edge by edge.
Fitment records
Document every dimension of a fitted setup.
Related Core Tire Dimensions Tools
View All 134 Subtools →Compare two tire sizes.
Compare several sizes together.
Estimate nominal overall diameter.
Calculate absolute and percentage differences.
Estimate nominal circumference.
Compare estimated rolling distances.