子午线轮胎（radial tire）的国际代号是“R”， 俗称为“钢丝轮胎”。
radial tire cord arrangement is different from the tire, radial tire cord is not mutually staggered, but with the tire section close to parallel, like the earth's meridian arrangement, cord angle is small, usually 0 degrees, not to maintain the intersection between the carcass cords, when the tire in the running process, the crown the surrounding stress increases, will cause the circumferential stretch, carcass radial gap. Close to the circumferential direction dealing with cord layer so the buffer layer of radial tire, 90 degrees intersect with the cord angle, generally 70 to 78 degrees, forming a rigid ring with hardly done, the whole tire fixed, tire circumferential deformation, the stress buffer 60% to 70% layer under the entire tire, become the main force components of radial tire, called radial tire belt. The main components of the diagonal tire are not on the buffer layer, and the internal stress of 80% to 90% is borne by the carcass ply. It can be seen that the design of the radial tire belt is very important, and it must have good rigidity. It can be made of the fiber material with large angle, high strength and not easy to stretch.