Radial ply tires have much more flexible sidewalls due to their construction. They use 2 or more layers of casing plies, with the cord loops running radially from bead to bead.
The sidewalls are more flexible because the casing cords do not cross over each other. However, a belt of 2 or more bracing layers must be placed under the tread.
The cords of the bracing layers may be of fabric, or of steel, and are placed at 12, to 15 degrees to the circumference line. This forms triangles where the belt cords cross over the radial cords.
The stiff bracing layer links the cord loops together to give fore and aft stability, when accelerating, or braking, and it prevents any movement of the cords during cornering.
The cord plies flex and deform only in the area above the road contact patch.
There are no heavy plies to distort, and flexing of the thin casing generates little heat, which is easily dispersed.
A radial ply tire runs cooler than a comparable cross-ply tire, and this increases tread life. Also, a radial tire has less rolling resistance as it moves over the road surface.
