Wheel Width Comparator
Compare rim width changes in inches and mm. See how much each edge moves at equal offset and how tire section width changes on the new rim.
Compare rim width changes.
Wheel Width Comparator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Wheel Width Comparator Works?
The Wheel Width Comparator works by converting the width change to millimeters and splitting the change between the inner and outer edges at the same offset. The tool uses 3 steps.
Enter both widths
Type the old and new nominal rim widths, for example 7.5 in and 8.5 in.
Convert and split
The comparator converts the 1.0 in change to 25.4 mm and moves each edge 12.7 mm (0.5 in).
Estimate tire growth
The comparator adds about 5 mm (0.2 in) of tire section width for each 0.5 in of extra rim width.
Wheel Width Comparator Formula
The Wheel Width Comparator formula is ΔEdge = (W_new − W_old) × 25.4 ÷ 2 on each side at equal offset.
ΔW = (W_new − W_old) × 25.4ΔE = ΔW ÷ 2ΔSW ≈ 5 mm × (ΔW_in ÷ 0.5)- W_old, W_new
- Nominal rim widths (in)
- ΔSW
- Change in tire section width on the new rim (mm)
Worked example
Going from a 7.5 in to an 8.5 in rim at the same offset moves each flange 12.7 mm (0.5 in). A 225 mm tire on the wider rim measures about 235 mm (9.25 in).
Wheel Width Comparator Conversion Table
The Wheel Width Comparator conversion table shows edge movement and approximate tire growth for 7 rim width changes.
| Width change | Total change | Each edge | Approx. tire width change |
|---|---|---|---|
| 7.0" → 7.5" | +12.7 mm (+0.5 in) | +6.3 mm | +5 mm |
| 7.5" → 8.0" | +12.7 mm (+0.5 in) | +6.3 mm | +5 mm |
| 7.5" → 8.5" | +25.4 mm (+1.0 in) | +12.7 mm | +10 mm |
| 8.0" → 9.0" | +25.4 mm (+1.0 in) | +12.7 mm | +10 mm |
| 8.5" → 9.5" | +25.4 mm (+1.0 in) | +12.7 mm | +10 mm |
| 9.0" → 10.0" | +25.4 mm (+1.0 in) | +12.7 mm | +10 mm |
| 8.0" → 7.0" | -25.4 mm (-1.0 in) | -12.7 mm | -10 mm |
What is Wheel Width Comparator?
A Wheel Width Comparator is a tool that compares the nominal width of 2 wheels and shows how the change affects clearance and tire shape. Rim width is the first number in a wheel size such as 8.5Jx18.
Rim width changes tire section width. Tire makers measure section width on a specified measuring rim, and each 0.5 in of rim width changes the tire by about 5 mm.
Each tire size has an approved rim width range. A 225/45 R17 tire typically accepts rims from 7.0 in to 8.5 in.
What are the uses of Wheel Width Comparator?
There are 4 main uses of the Wheel Width Comparator, including tire stretch avoidance and clearance checks.
Tire stretch avoidance
Keep the rim inside the tire's approved range.
Clearance checks
See how much a wider wheel moves each edge.
Sidewall shape
Predict a flatter or rounder sidewall on the new rim.
Width upgrades
Pick a wider wheel that still suits the stock tire.
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.