Tire Section Width Comparator
Compare the nominal section width of two tires in mm and inches, and see how much the sidewall moves inward and outward on each side.
Compare nominal section widths.
Tire Section Width Comparator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Tire Section Width Comparator Works?
The Tire Section Width Comparator works by reading the first number of each size code and splitting the width change equally between the inner and outer side of the tire. The tool uses 3 steps.
Enter both widths
Type the stock width (for example 225 mm) and the new width (for example 245 mm).
Compute the gap
The comparator subtracts 225 from 245 for a 20 mm (0.79 in) wider tire.
Split per side
The comparator divides the gap by 2 and shows 10 mm (0.39 in) closer to the strut and 10 mm closer to the fender, with the same wheel offset.
Tire Section Width Comparator Formula
The Tire Section Width Comparator formula is ΔW = W₂ − W₁, and the change per side is ΔW ÷ 2.
ΔW = W₂ − W₁ΔW_side = ΔW ÷ 2W_in = W ÷ 25.4ΔW% = ΔW ÷ W₁ × 100- W₁, W₂
- Nominal section width of stock and new tire (mm)
- ΔW_side
- Movement of each sidewall (mm)
Worked example
Moving from 235 mm to 255 mm adds 20 mm (0.79 in), or 8.5% of width. Each sidewall moves 10 mm (0.39 in) outward from the wheel centerline.
Tire Section Width Comparator Conversion Table
The Tire Section Width Comparator conversion table converts 14 standard section widths into inches and centimeters and shows the per-side change against a 225 mm tire.
| Section width | Inches | Centimeters | Change vs 225 mm | Change per side |
|---|---|---|---|---|
| 185 mm | 7.28 in | 18.5 cm | -40 mm | -20.0 mm |
| 195 mm | 7.68 in | 19.5 cm | -30 mm | -15.0 mm |
| 205 mm | 8.07 in | 20.5 cm | -20 mm | -10.0 mm |
| 215 mm | 8.46 in | 21.5 cm | -10 mm | -5.0 mm |
| 225 mm | 8.86 in | 22.5 cm | +0 mm | +0.0 mm |
| 235 mm | 9.25 in | 23.5 cm | +10 mm | +5.0 mm |
| 245 mm | 9.65 in | 24.5 cm | +20 mm | +10.0 mm |
| 255 mm | 10.04 in | 25.5 cm | +30 mm | +15.0 mm |
| 265 mm | 10.43 in | 26.5 cm | +40 mm | +20.0 mm |
| 275 mm | 10.83 in | 27.5 cm | +50 mm | +25.0 mm |
| 285 mm | 11.22 in | 28.5 cm | +60 mm | +30.0 mm |
| 295 mm | 11.61 in | 29.5 cm | +70 mm | +35.0 mm |
| 305 mm | 12.01 in | 30.5 cm | +80 mm | +40.0 mm |
| 315 mm | 12.40 in | 31.5 cm | +90 mm | +45.0 mm |
What is Tire Section Width Comparator?
A Tire Section Width Comparator is a tool that compares the sidewall-to-sidewall width of two tires and shows the change on each side of the wheel. Section width is the first number in a metric size, measured in millimeters on the specified measuring rim.
Section width is not tread width. The tread face is 15 to 30 mm (0.6 to 1.2 in) narrower than the section width on most passenger tires.
Section width changes 5 mm (0.2 in) for every 0.5 in (12.7 mm) change in rim width. The Rim-Dependent Section Width Estimator handles that correction.
What are the uses of Tire Section Width Comparator?
There are 5 main uses of the Tire Section Width Comparator, including strut clearance checks and fender fit checks.
Strut clearance checks
Compare half the width gain with the measured gap to the strut or control arm.
Fender fit checks
Compare half the width gain with the space under the fender lip.
Staggered setups
Compare narrower front tires with wider rear tires.
Winter narrowing
Measure the width reduction of a narrower winter tire.
Rim range checks
Check the new width against the rim width range in the tire maker's data book.
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