Rim-Dependent Section Width Estimator

This estimator works by adding about 5 mm (0.2 in) of section width for every 0.5 in the rim is wider than the measuring rim. It subtracts the same amount for narrower rims.

1. Enter the tire's nominal width, for example 225 mm.
2. Enter the measuring rim, for example 7.0 in.
3. Enter your rim width, for example 8.0 in.
4. Read the estimated width: 235 mm (9.25 in).

The formula is Estimated Width = Nominal Width + ((Rim − Measuring Rim) ÷ 0.5) × 5.08 mm.

5.08 mm is 0.2 in. Worked example: a 285 mm tire measured on 9.0 in and mounted on 10.0 in is about 285 + 10.2 = 295 mm wide.

The rule holds only inside the approved rim range.

The conversion table estimates section width for 5 tires on 5 rim widths from 6.0 in to 10.0 in. Values outside each tire's approved range are shown for comparison only.

The 225 mm tire runs from about 215 mm on a 6.0 in rim to 255 mm on a 10.0 in rim.

The Rim-Dependent Section Width Estimator is a tool that predicts a tire's real width on a rim different from its measuring rim. The nominal width in the size code applies only on the measuring rim.

Wider rims pull the sidewalls apart and add width; narrower rims pinch them and remove width. The 0.2 in per 0.5 in rule is a widely used industry estimate.

This estimator has 4 uses: clearance checks, appearance planning, tire comparisons and wheel selection.

• Check clearance: Use the real width for strut and fender checks.
• Plan appearance: Predict a squared or stretched sidewall look.
• Compare tires: Line up widths on your rim.
• Select wheels: See how wheel width changes tire width.