RCRAMER.COMTires: Sidewall Markings
Calculating Tire Size
The first number is the width of the tire in millimeters, measured from sidewall to sidewall. To convert to inches, divide by 25.4 In the example above, the width is 185mm or 7.28".
The second number is the aspect ratio. This is a ratio of sidewall height to width. In the example above, the tire is 7.28" wide, multiply that by the aspect ratio to find the height of one sidewall. In this case, 185x0.60=111mm or 7.28"x0.60=4.36".
The last number is the diameter of the wheel in inches.
To figure the outside diameter of a tire, take the sidewall height and multiply by 2,(remember that the diameter is made up of 2 sidewalls, the one above the wheel, and the one below the wheel) and add the diameter of the wheel to get your answer.
Example...185/60R14 85H or 185/60HR14185mm x .60=111mm x 2=222mm + 355.6mm(14")= 577.6mm or 22.74"
| Speed Rating: | |||
| N | 87 MPH | U | 124 MPH |
| P | 93 MPH | H | 130 MPH |
| Q | 99 MPH | V | 149 MPH |
| R | 106 MPH | Z | 149 MPH |
| S | 112 MPH | W | 168 MPH |
| T | 118 MPH | Y | 186 MPH |
