HOW TO CALCULATE TYRE DIMENSION?
Example size: 225/45R17 The first three numbers in a typical size (225/45R17) are the tire's indicated section width in millimeters, measured from sidewall to sidewall
If you are familiar with measurements in inches, the section width in millimeters can be converted into inches by dividing it by 25.4. For example:
225mm / 25.4 = 8.86"
The second pair of numbers (225/45R17) is the tire's aspect ratio or profile. This is a ratio of sidewall height to section width. The section height's measurement can be calculated by multiplying the section width by the aspect ratio. The answer will be the height of one sidewall. For example:
225mm x 0.45 = 101.3mm 8.86" x 0.45 = 3.99"
The last number (225/45R17) is the diameter of the wheel in inches.
If you are familiar with measurements in the metric system, the wheel diameter can be converted into millimeters by multiplying it by 25.4. For example:
17" x 25.4 = 431.8mm
To calculate the overall diameter of a tire, the sidewall height must be multiplied by 2 (remembering that the tire diameter is made up of 2 sidewalls, the one above the wheel and the one below the wheel touching the ground) and add the diameter of the wheel.
101.3mm + 101.3mm + 431.8mm = 634.4mm 3.99" + 3.99" + 17" = 24.98"
Please check also the following link where you can have a Tyre conversion table for comparison. But by default we would like it to be in mm and in option to have it in inches and Percentage as well.