Tire Diameter Calculator

OEM tires are engineered to stop, turn, and just act in a normal, or safe, manner. On the other hand you can buy insanely stupid wide tires found on customs that won't go around corners...Everyone has a purpose. Show, go, or cruise. Your motorcycle tires have government mandated information on the sidewall that can be used to calculate their diameter.

Example: 185/60HR14

Rim Diameter: In this case it is 14

Section Width: In this case it is 185. The first number is the width of the tire in millimeters, measured from sidewall to sidewall. If your dimension is in inches, multiply by 25.4

Aspect Ratio: In this case it is .60. The second number is the aspect ratio. This is a ratio of section height height to section width.

 To Calculate Speed, Gearing, or Trail: How tall is my tire?

Formula: Diameter in Inches = Rim Diam Inches + [ (2 x Aspect Ratio x Section Width) / 25.4]

Example # 1: 200/55R18 Tire:
Tire Height 26.66" = 18 + [(2 x 0.55 x 200)/25.4]

Example # 2: 300/30R18 Tire:
Tire Height 25.09" = 18 + [(2 x 0.30 x 300)/25.4]

 Rim diameter: Inches: i.e. 15, 16, 17, 18, 19, 21, 23 etc. Aspect Ratio: i.e. 0.55, 0.60, 0.70 etc. Section Width: i.e. 170, 200, 240, 300 etc.

Inches Tall________________________

You have to know the diameter of your tire when making speed, gearing, or trail calculations. It is often not easy to "eyeball" a measurement, even with a tape measure. Trying to get tire data is often not easy.

Simply read the tire specifications on your sidewalls and calculate the tire's diameter. Rubber down, paint up. Bonneville.