How do I calculate Tire Height and Rotations Per Mile?
A tire’s theoretical height in inches is calculated as follows: Height = (Width x (Ratio/100) x .03937 x 2) + Rim Diameter The width multiplied by the aspect ratio over 100 gives the height in millimeters, multiplying by .03937 converts to inches, and doubling this accounts for the fact that there’s tire at the bottom and the top of the rim. Rotations Per Mile (RPM) can be calculated as follows: RPM = (inches per mile) / Tire Circumference = (5280*12) / (Height*3.1416) = 20,168 / Height Some sample calculations of tire height and RPM are shown below: Height RPM Error @60MPH Note: 205 60 15 24.69 817 – 60.0 Stock size 225 55 15 24.74 815 0.2% 60.1 Wider tire on stock 225 50 16 24.86 811 0.7% 60.4 Plus One 245 45 16 24.68 817 0.0% 60.0 Plus One 245 40 17 24.72 816 0.1% 60.1 Plus Two 245 35 18 24.75 815 0.3% 60.2 Plus Three 185 65 15 24.47 824 -0.9% 59.5 Snow tire alternative It may be helpful to set up a simple spreadsheet to determine options. Height and RPM calculations are given above
