What is the meaning of tire speed index ?

Why the higher the speed index, the more expensive the tires?

In order to prevent the danger of unrestricted acceleration of cars on the highway, the concept of speed index was proposed in the 1960s. Nowadays, the speed index of most passenger car tires is between S and Y, that is to say, the maximum withstand speed is between 180-300 km/h. It can be seen from the speed grade table that the tire speed grade starts from M, the lower the letter represents the higher the performance, and interestingly, there is an H between the grades U and V, that is, H stands for ” high performance”.
Although the current maximum speed on general domestic highways is controlled at 120km/h, because the tires are rubber products, with the increase of years, the carrying capacity becomes weaker and weaker, and the increase in road temperature will also greatly reduce the maximum speed level. . Therefore, in general, the tire equipment manufacturers will be several levels higher than the speed limit of 120 kilometers to ensure the safety of the tires.

The higher the speed index, the higher the tire design and material requirements. Under normal circumstances, the higher the load index, the higher the speed index and the better the performance of the tires of the same brand and the same size specifications, the more expensive the price will be. “Take Michelin as an example. For tires of the same size, 91V tires will be 30 or 40 yuan more expensive than 91H tires.”

According to internationally accepted standards, the speed index of car tires must be higher than the maximum speed per hour designed for the car. The design maximum speed of A0-class cars with 70,000-100,000 yuan is generally 200 kilometers, and should be equipped with H-class tires with a maximum speed of 210 kilometers per hour; A-class cars with 100,000-150 thousand yuan should be equipped with V-class tires with a maximum speed of 240 kilometers per hour; 20 The 300,000 yuan B-class sedan is equipped with W-class tires with a maximum speed of 270 kilometers per hour.

The effect of speed index on tire performance

The tire will be squeezed and deformed during the rolling process, so it will generate heat. This is the reason why under-inflated tires are prone to “runaway”, because there is not enough tire pressure support, the deformation of the tire during a round of rolling is serious, which not only generates more heat, but also severely destroys the structure of the tire.
Even with fully inflated tires, this situation still exists, but to a lesser degree. In order to better alleviate tire deformation and heat generation, high speed grades will enhance the shoulder and tread pattern, which not only reduces the deformation of the tire during rolling, but also the performance of the tire’s contact surface with the ground is more stable. In layman’s terms, tires with high speed ratings have stronger grip when turning the vehicle.

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