1, flatness ratio
refers to a flatness ratio of the maximum cross-sectional ratio of the width to the height measured from the rim of the tire tread, expressed as a percentage, i.e. a percentage of the height width. At 205 / 60R15 size tires, for example, the maximum width of the cross section is 205 mm, an inner diameter of the tire 15 inches, flatness ratio of 60. 
In general, more use is currently made saloon multi-width or small, a small inner diameter of the tire and a high flatness ratio. Since the flatness ratio of the higher tire sidewall long, strong buffering capacity, relatively high comfort, but the feeling of the road surface is poor, weak lateral resistance during turning. Conversely, lower than the flat, large inner diameter of the tire, because of the shorter sidewalls, tread wide. Therefore, the ground area, the tires can withstand the pressure also big, the road surface reaction is very sensitive, strong lateral resistance when turning, the vehicle handling is greatly enhanced.
Generally, when the vehicle is shipped from the factory with the tire manufacturers are tested after repeated selecting optimal specifications . If the owner wants to replace the tire size, must be conducted under the guidance of professionals, can not be arbitrary and, because it involves a lot of questions, a little negligence may cause harm to traffic safety. Further, lower than the flat tires appear more “delicate” number, should be more attention and care during use.