Tire Sizes Explained

Section width of tire (Example: P 225/45R17 91V)

• The three digits following the service type prefix (if present) tell us the cross-sectional width of the tire in millimeters.
• Calculation : dividing the width in millimeters by 25.4

Aspect ratio of sidewall (Example: P225/ 45 91V)

• The two-digit number that usually follows the tire's section width tells us the aspect ratio, or tire profile measurement.
• Calculation : multiplying the sidewall distance in inches by 0.45

Tire and wheel diameter (Example: P225/45R17)

• Tires usually come in the following widths (in inches): 8, 10, 12, 13, 14, 15, 17, 18, 19, 20, 22, 23, 24, 26, and 28.

Unique wheel diameters

• These sizes are usually 14.5, 15.5, 16.5, 17.5, and 19.5 inches, and an example would be 33x12.5R16.5 118R.

Internal construction (example: P225/45R17 91V)

• R means the tire has radial construction
• D means the tire has a bias ply construction
• B means the tire is in belted tires

Speed rating (Example: P225/45R17 91 V)

• The only speed rating still included in the tire size is the Z rating (sports cars)

Service description rating (Example: P225/45R17 91V)

• The service description rating is mandatory for all speed ratings (except Z-rated tires) and appears at the end of the tire's size brand. The service description is used to identify the tire's load index and speed rating