Pneumatic radial tire

Claim 1

A pneumatic radial tire comprising a carcass, a tread, a reinforcing belt layer having a structure composed of at least three metallic cord layers, and narrow grooves extending in the circumferential direction of the tire respectively provided on left and right shoulder portions of said tread surface, wherein among said layers constituting said reinforcing belt layer, a second reinforcing belt layer and a third reinforcing belt layer spaced outwardly from said carcass towards said tread cross each other at a cord angle of 10° to 30° relative to the circumferential direction of the tire; and a first reinforcing belt layer located outwardly adjacent said carcass towards said tread has a cord angle of 40° to 75° relative to the circumferential direction of the tire and is split into axially spaced apart left and right portions in the central region of a crown and provided with an organic fiber cord layer having a cord angle of 0° to 10° relative to the circumferential direction of the tire between said left and right split portions of said first reinforcing belt layer, said narrow groove having a depth h as determined in the radial direction of the tire, and a distance d 1 measured between the internal edge on said shoulder side of an opening portion of said narrow groove and the radially outermost surface of said shoulder portion as determined along a parallel line to the surface of said tread, and a distance d 2 measured between the internal wall surface on the shoulder side of the bottom of said narrow groove and the radially outermost surface of said shoulder portion as determined along a parallel line to the surface of said tread, wherein d 1 is less than 15 mm and is smaller than d 2 , and a shape factor m defined by the following equation is 0.8 to 1.2: ##EQU3##