Tire Sizes Decoded
185 / 60 R 14
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 , the width is 185mm or 7.28″. The Second number is the aspect ratio. This is the ratio of sidewall height to width. In the example, the tire is 7.28″ wide, multiply that by the aspect ratio to find the height of one sidewall. In this case, 185×0.60=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 and below the wheel) and add the diameter of the wheel to get your answer.
Overall Diameter (Example): 185mm x 0.60 = 111mm x 2 = 222mm + 14″ x 25.4 (355.6mm) = 577.6mm (/ 25.4 to get inches) or 22.74″
