how to measure tire width
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. The second pair of numbers (225/45R17) is the tire's aspect ratio or profile. This percentage represents the ratio of sidewall's section height to the tire's section width.