Heavy duty pneumatic radial tires

Abstract

A heavy duty pneumatic radial tire comprises a carcass of a substantially radial construction composed of at least one rubberized ply layer containing cords embedded therein and a belt superimposed about said carcass for stiff reinforcement beneath a tread and composed of at least two rubberized ply layers each containing metal cords embedded therein, said metal cords of which being crossed with each other at a relatively small angle with respect to the circumferential direction of tire, and said tread being provided with a plurality of continuous or discontinuous zigzag circumferential ribs defined along the widthwise direction of tire by at least three, substantially zigzag main grooves extending circumferentially of said tread, said main grooves comprising one or a pair of central circumferential grooves located at a substantially central region of said tread and a pair of outside circumferential grooves defining each of outermost ribs of said tread. In this tire, the central circumferential groove has such a symmetrical cross-sectional shape with respect to a center line of said groove that an inclination angle of a groove wall of said groove with respect to a normal line drawn from an outer surface of said tread and passing an edge of said groove in the cross section perpendicular to said groove wall is made relatively large in a region extending from the groove bottom to at least 50% of groove depth, and the outside circumferential groove has such an unsymmetrical cross-sectional shape with respect to a center line of said groove that an inclination angle of an outer groove wall of said groove in the rotation axial direction of tire is made relatively large and an inclination angle of an inner groove wall of said groove in a region extending from the outer surface of said tread to at least 10% of groove depth is made smaller than that of said outer groove wall.