The wheels of cars generally use radial tires. The specifications of radial tire include width, aspect ratio, inner diameter and speed limit symbol. Take Toyota CROWN3.0 as an example, its tyre size is 195/65R15, which means that the width between the two sides of the tire is 195 mm, 65 means the aspect ratio, and "R" means RADIAL, which means radial tire. 15 is the inner diameter of the tire, measured in inches. Some tires are also marked with speed limit symbols, which are represented by letters such as P, R, S, T, H, V and Z respectively.

In particular, it should be pointed out that the aspect ratio means the percentage of tire sidewall height to tire width. The aspect ratio of modern cars is between 50 and 70. The smaller the value, the flatter the tire shape. With the increase of vehicle speed, in order to reduce the center of gravity and axis of the car, the diameter of the tire is shrinking. In order to ensure sufficient bearing capacity and improve driving stability and grip, the widths of tires and rims have to be continuously increased. Therefore, the cross-sectional shape of the tire has developed from the original approximate circular shape to the flat elliptical shape.

In recent years, cars have realized radial tire tubeless, commonly known as "atomic tire". This kind of tire is not easy to gather heat when driving at high speed. When the tire is punctured by nails or sharp objects, it leaks slowly and can continue driving for a certain distance. In addition, the atomic tire also has the advantages of simplifying the production process, reducing weight and saving raw materials. Therefore, assembling atomic tires has gradually become a trend in the field of cars.