The air leakage rate of tires is one of the important factors affecting the driving comfort of automobiles. So what is the air leakage rate of the tire? Flatness ratio: refers to the cross-sectional height of a tire, which accounts for the percentage of its maximum cross-sectional width. Simply put, it is the length-width ratio of the tire. For example, the size marked on the tire is 225/55R 18. The explanation of this specification is that the tire section width is 225mm, the flatness is 55, and the rim size is 18 inch. For different models, manufacturers will match the corresponding tire models according to their different design requirements, manufacturing costs and body weight. The smaller the flat rate of a tire, the greater the percentage between the height and width of its cross section. Simply put, the lower the tire height. This kind of tire is characterized by large friction area with the ground and low pressure on the tire, so the wear and rolling resistance of the tire are relatively small, which can provide better lateral stability and handling. Therefore, in some mid-to high-end models, performance cars or sports cars, low flat tires are often used, which can not only reduce the center of gravity of the whole vehicle and improve the driving stability, but also make the car look particularly beautiful and domineering if equipped with large-size wheels. However, tires with low deflation rate also have their own shortcomings, such as relatively poor comfort. There are two very important characteristics to measure tire performance, grip and comfort, which refer to the lateral force and longitudinal force of tire respectively. The greater the lateral force a tire can bear, the better its grip, the greater the longitudinal force it can bear and the better its comfort. The lateral force mainly depends on the width of the tire, and the longitudinal force mainly depends on the height of the tire, which is what we call the flattening rate in this paper. Therefore, although the low flat tire has a large contact area with the ground, it can bear a large lateral force and has a strong grip on the ground, but it also sacrifices some comfort. This is like a pair of cloth shoes with a low puncture and a pair of sports shoes with a high puncture. The comfort of natural cloth shoes is worse than sports shoes. Moreover, tires with low deflation rate are easier to bulge because they are thin and pitted. After talking about low flat tires, the performance of high flat tires and low flat tires is basically the opposite. When we divide the boundary between the two, we usually take the number 45 as the dividing line, and those below 45 are classified as low flat tires. On the contrary, since. Finally, some people may ask, since the comfort of low flat tires is low, why do mid-to high-end cars prefer to use low flat tires? At the beginning of the article, it has been said that the air leakage rate of tires is one of the important factors affecting the comfort of automobiles. Since it is one of them, it shows that there are other factors that will affect the comfort of the car. Mid-to-high-end models can be optimized in suspension, chassis and seats to make up for the comfort problems caused by low flat tires.