What do the numbers and letters on tires mean?
3 Answers
The numbers and letters on tires, taking 225/45R17 as an example: Before the letter 'R', there are '45' and '225', where '45' represents the aspect ratio of the tire. The aspect ratio is the ratio between the tire's section height and section width; '225' represents the section width of the tire; '17' represents the diameter of the wheel rim; and 'R' indicates that it is a radial tire. Tires are circular elastic rubber products assembled on various vehicles or machinery for rolling on the ground. They are usually mounted on metal rims to support the vehicle body, cushion external impacts, ensure contact with the road surface, and guarantee the vehicle's driving performance.
Last time my neighbor was confused by the numbers when changing tires, and I explained it to him. For a marking like 215/55 R17 91V — 215 is the tire width in millimeters, 55 is the aspect ratio (the sidewall height is 55% of the width), R stands for radial construction, and 17 corresponds to the wheel diameter in inches. 91 is the load index (615 kg), and V is the speed rating (up to 240 km/h). The last four digits of the DOT code on the sidewall indicate the production week/year, for example, 3822 means the 38th week of 2022. When choosing tires, these parameters must match the original specifications, otherwise, it can affect the speedometer's accuracy or even cause rubbing against the wheel arch. Pay extra attention to the special parameters on spare tires.
My daughter also asked about tire codes when learning to drive. Simply put, for example, a tire marked P225/60R16 95H: P stands for passenger car tire, 225 is the section width in millimeters, 60 is the aspect ratio (60%), R means radial tire, and 16 is the rim diameter it fits. 95 is the load index (690 kg), and H indicates a maximum speed of 210 km/h. If the wear indicator bars in the tread are flush with the tire surface, it's time to replace them. For winter tires, look for the snowflake symbol, and the speed rating is usually T or H. Load index is crucial; last time our family went on a trip fully loaded with luggage, I specifically chose tires with a 94 load index.
