Tire size calculator

Current tire size


/ R

New tire size


/ R

235/50 R18 vs 205/70 R15 comparison results:

Old New Diff %
Overall Diameter 27.25" 26.30" -0.95" (-24.20 mm) -3.50% Smaller sign. Arrow down
Width 9.25" (235.00 mm) 8.07" (205.00 mm) -1.18" (-30.00 mm) -12.76% Smaller sign. Arrow down
Sidewall Height 4.63" (117.50 mm) 5.65" (143.50 mm) +1.02" (+26.00 mm) +22.13% Bigger sign. Arrow up
Rim Diameter 18" 15" -3" -16.67% Smaller sign. Arrow down
Ground Clearance -0.48" (-12.10 mm) Smaller sign. Arrow down
Circumference 85.61" (217.46 cm) 82.62" (209.86 cm) -2.99" (-7.60 cm) -3.50% Smaller sign. Arrow down

Speedometer difference

Original Speed (mph) New Speed with New Tires (mph)
20.019.3
30.029.0
40.038.6
50.048.3
60.057.9
70.067.6
80.077.2
90.086.9
100.096.5

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Welcome to our handy wheel and tire size calculator!

Put your current tire size(width, aspect ratio, and diameter) into the first form, then your desired size into the second form and you will get the difference between the new and tire size. Also, determine the speedometer reading difference and the actual speed with a new set of tires. You can use both metric and flotation sizes for your vehicle.

Our tire calculator could help decide whether tires and wheels will fit into your car. If you need to compare tires by brand and model use our tire comparison tool.