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Compare two tire sizes to see diameter change, sidewall differences, revs per mile, and speedometer error. Use this calculator when planning plus-size or minus-size fitment for street, off-road, or performance setups.
Last updated: April 17, 2026
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Diameter Change
+0.06 in
Diameter % Change
+0.21%
Revs/Mile Change:
-0.21%
Actual Speed:
60.12 mph
Calculated Diameters:
Current: 28.52 in | New: 28.57 in
Fitment Tips:
Computed values
Sidewall, Diameter, Circumference
Output
Revs/Mile Delta
Use case
Indicated vs Actual Speed
For 225/65R17 to 245/60R17 at 60 mph indicated speed:
60.12 mph actual
Each tire code is converted into dimensions. Sidewall height comes from width and aspect ratio, then total diameter is wheel diameter plus twice the sidewall. From diameter, circumference and revs per mile are calculated to estimate gearing and speedometer impact.
Diameter = Wheel + 2 * SidewallActual Speed = Indicated * (New Diameter / Current Diameter)Diameter change: +0.06 in (0.21%)
60.12 mph
Estimated actual speed at 60 mph indicated
Share it with drivers and builders planning wheel and tire changes.
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