Redmoon Converters Compare any two tire sizes (e.g. 225/45R17 vs 245/40R18) for overall diameter, circumference, speedometer error % and clearance change.
| Metric | Tire A | Tire B | Δ |
|---|
P-metric format W/AR-D: sidewall (mm) = section width × aspect / 100. Overall diameter (mm) = 2 × sidewall + rim × 25.4. Circumference = π × diameter. Revs/mile = 1 609 344 / circumference.
Speedometer error at indicated speed = (B.diameter − A.diameter) / A.diameter × indicated. Positive = true speed higher than shown when fitting tire B.
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