_20 indicates that the tire has a radial structure and the outer diameter of the rim is 20 inches. Tire size is usually represented by a set of numbers, with the former number representing the tire section width and the latter number representing the rim diameter in inches. For example, 165/70R 14 represents a radial tire with a tire width of 165mm, a flat rate of 70, and a rim diameter of 14 inch. Some tires also contain other letters or symbols with special meanings: "X" stands for high pressure tire; "c" stands for enhanced type; "b" means oblique; "One" refers to the low-pressure tire.
_ and S are abbreviations for mud and snow, respectively, indicating that this kind of tire is suitable for use on icy and muddy roads. The sidewall of some tires is marked with the words "arrow" or "outside" to indicate the direction of tire rotation. If there is a small umbrella sign on the tire wall, it means that this kind of tire is suitable for driving on rainy days or wet roads.