What does the tire model zr mean?

[Clinton]

Tire model zr is a tire speed rating symbol, indicating the maximum speed at which the tire can carry the specified load under specified conditions. The letter z represents that the tire is a high-speed tire capable of operating at speeds exceeding 240 kilometers per hour, while r stands for radial tire. Tires are categorized by usage into truck tires, passenger car tires, and mining tires. Among these, the ply rating of truck tires does not refer to the actual number of layers but rather to tires made with high-strength material cords for the carcass, whose load-bearing performance is equivalent to that of tires made with cotton cord carcass plies. This is because cotton cords are used to make the carcass plies, hence the international convention uses cotton cord plies as the benchmark for indicating tire ply ratings.