A radial tire with a split structure in the first belt layer provided with an organic fiber cord layer in the split structure and having a narrow groove extending in the circumferential direction of the tire and provided in each of both shoulder portions of the surface of a tread, wherein the narrow groove has a depth h determined in the radial direction of the tire, and a distance d.sub.1 measured between the internal edge on the shoulder side of an opening portion of the narrow groove and the radially outermost surface of the shoulder portion as determined along a parallel line to the surface of the tread, and a distance d.sub.2 measured between the internal wall surface on the shoulder side of the bottom of the narrow groove and the radially outermost surface of the shoulder portion as determined along a parallel line to the surface of the tread, wherein d.sub.1 is less than 15 mm and is smaller than d.sub.2, and a shape factor m defined by the following equation is 0.8 to 1.2: ##EQU1##