What do the numbers and letters on tires mean?

[MacJoshua]

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.

[CarolineAnn]

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.

[DelElena]

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.

[VanDelilah]

Remember my first tire change, the veteran mechanic taught me to recognize these markings. Focus on four key parts: size like 195/65 R15 (width/aspect ratio/wheel diameter), construction identifier R (radial tire), load index and speed rating. 89T means a load capacity of 580kg and maximum speed of 190km/h. The TWI mark pointed by the triangle symbol on the sidewall indicates tread wear indicators. Pay special attention to the four-digit production date after DOT - 0219 means the second week of 2019. Always check tread depth before rainy season, replace if below 1.6mm.

[McGrace]

With twenty years of experience in car repair, I find that tire parameters are the most misunderstood by customers. For example, 205/55R16 91W: 205mm tire width, 55% aspect ratio, and 16-inch wheel diameter. The load index 91 corresponds to 615kg (suitable for five passengers), and the speed rating W indicates a maximum speed of 270km/h. Pay special attention to the directional arrow on the sidewall indicating rotation direction—installing it backward will increase tire noise. Winter tires feature a mountain snowflake symbol, while summer tires are marked M+S. Spare tires often have a yellow warning indicating a speed limit of 80km/h. Tire lifespan is typically around five years, as they harden and crack even if the tread depth remains sufficient.

[LaCarter]

A friend who's into car modifications taught me the ins and outs of reading tire codes. Taking 245/40ZR18 as an example: ZR is the symbol for high-performance tires, often paired with W/Y ratings (270/300 km/h top speed). The tire pressure marking MAX PRESS 300kPa indicates the maximum cold inflation pressure. Pay special attention to the 3T indices—Traction A (braking on wet surfaces), Temperature A (heat resistance), and Treadwear 280 (standard tires rated 100 last 48,000 km). When modifying, increasing the section width by more than 1 inch may cause rubbing against the suspension, and a speed rating that's too low can affect the vehicle's top speed performance.