๐ Automotive
Tire Size Calculator
Tire sizes are written as width, aspect ratio and rim diameter โ a 225/45R17 is 225 mm wide with a sidewall 45 percent of that width on a 17-inch wheel. Changing overall diameter throws off the speedometer because the car counts wheel revolutions.
How it works
New tire width
New aspect ratio
New wheel diameter
Original width
Original aspect ratio
Original wheel diameter
New tire diameter
Original tire diameter
Diameter difference
Speedometer error at 60 mph
Fitment check
Actual speed when the speedo reads 60
Frequently asked questions
How do I use the Tire Size Calculator?
Fill in the fields above โ the result recalculates instantly as you type. Everything runs in your browser, so the values you enter are never collected or stored.
Is this calculator free?
Yes. It is completely free, requires no account, and works on phones, tablets and desktops.