ZovaTool

Tire Size Calculator

Tire 1 (Stock)

225/65 R17
Diameter
28.52″
724 mm
Revs/mi
707

Tire 2 (Compare)

245/45 R18
Diameter
26.68″
678 mm
Size Diff
-6.43%
Recalibrate speedometer

Speedometer Error

With Tire 2, actual speed = 56.1 mph when reading 60 mph

How to use the Tire Size Calculator

  1. Read the sidewall code (e.g. 225/65R17).
  2. Enter width (mm), aspect ratio (%) and rim diameter (in).
  3. Get overall diameter, sidewall height, circumference and revolutions per mile.
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Reading a tire sidewall

Format: W/A R D. W = section width in mm. A = aspect ratio (sidewall as % of width). D = rim diameter in inches.

Upsizing without keeping diameter close throws off your speedometer and ABS calibration.