Tire Size Comparison Calculator
Compare two tire sizes of the conventional width/aspect-ratio/rim-diameter format. The result is geometrical only: actual fitment also depends on the vehicle, wheel width, load index, speed rating and manufacturer guidance.
Enter your figures
Use your own values for a meaningful estimate.
How this calculation works
Sidewall height (mm) = tire width ร aspect ratio รท 100. Overall diameter (mm) = 2 ร sidewall height + rim diameter (in) ร 25.4. Circumference = ฯ ร diameter.
Worked example
Comparing 205/55 R16 to 215/55 R16 yields diameters of 631.9 and 642.9 mm, a +1.74% change. At an indicated 100 km/h, actual speed could be about 101.74 km/h if calibration is unchanged.
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Frequently asked questions
Does a close diameter guarantee tire fitment?
No. Verify clearance, original equipment specifications, load and speed ratings with a qualified fitter.
Is the speed result exact?
No. It assumes the speed display was calibrated to the original tire size.