Center block side rib tread pattern for heavy vehicle radial tires

In a pneumatic radial tire for heavy vehicles having a center block-side rib type tread pattern, comprising a reinforcement structure for rigidly reinforcing that portion of the tire which is located directly beneath a tread by means of a carcass including cords arranged substantially in a radial plane and a belt layer including metal wire cords and superimposed about the carcass, two relatively wide main grooves extending in circumferential direction of the tire and spaced apart from each other in the widthwise direction of the tire by a distance which is within a range between at least 20% of the tread width and at most 60% of the effective width of the belt layer, these two main grooves dividing the tread into a center region and two side regions, a relatively narrow zigzag or substantially zigzag auxiliary groove extending in circumferential direction of the tire and dividing each of the three regions into two portions and a branch groove located in the center region of the tread and connecting the zigzag auxiliary groove to the right and left main grooves alternately, the branch groove dividing the center region tread also in the circumferential direction, of the improvement wherein each of said main grooves has a width which is 5 to 9% of the width of the tread and is substantially U-shaped in cross-section and in which at least those edges of said main grooves which define said center region consist of a bent or wavy line having an allocated pitch of 0.3 to 1.3 times the width of said main grooves and a swing width within a range from 0.1 to 1.0 times the width of said main groove, said main grooves forming substantially a direct through drainage path, and in which said branch groove has a depth which is far shallower than and corresponds to 14 to 36% of the depth of said main groove, said branch grooves together with said main and auxiliary grooves defining the blocks in the center region of the tread.