According to tire specifications, the speed rating indicates the maximum speed at which a tire can carry a specified load under defined conditions. Letters from A to Z represent certified speed ratings ranging from 4.8 km/h to 300 km/h. In recent regulations standardized for tire labeling, all speed ratings except the continuously variable Z rating include both speed symbols and load indexes in their usage instructions. The speed symbol on a tire, also known as the tire speed rating, refers to the maximum permissible speed allowed for use under specified road surface conditions, nominal rim diameter, and within a defined time period. On tires, the letter J represents 100 km/h, K represents 110 km/h, L represents 120 km/h, M represents 130 km/h, N represents 140 km/h, P represents 150 km/h, Q represents 160 km/h, R represents 170 km/h, and S represents 180 km/h. Additionally, T, U, H, V, and Y respectively represent 190 km/h, 200 km/h, 210 km/h, 240 km/h, and 270 km/h. ZR indicates speeds exceeding 240 km/h. Tires are primarily composed of polymer composite materials, and temperature increases accelerate rubber aging. When a vehicle travels at high speeds, the entire tire's temperature rises, leading to accelerated tread wear. Every tire has its designed critical speed. When high-speed driving reaches this speed, the tire exhibits a "standing wave" phenomenon, which is the tire's "critical speed." Continued use under these conditions may result in a risk of tire blowout.
