Heavy duty pneumatic radial tires

Claim 1

In a heavy duty pneumatic radial tire with an improved service durability of the bead portion comprising a toroidal carcass composed of at least one cord ply containing aromatic polyamide fiber cords arranged parallel with each other in a direction substantially perpendicular to the equatorial plane of the tire and wound around a bead core from the inside of the tire toward the outside thereof to form a turnup portion, a belt superimposed about a crown region of the carcass and composed of at least three cord layers, a bead portion reinforcement consisting of a stiffener disposed between the carcass and its turnup portion and composed of a base portion of relatively hard rubber stock contacting with the bead core and a thickness-reducing portion of a relatively soft rubber stock integrally united with the base portion, a main chafer extending from a level lower than an upper end of the turnup portion along the turnup region of the carcass toward the inside of the tire and made from aromatic polyamide fiber cords, a plural layer auxiliary chafer made from cords having a modulus of elasticity lower than that of the main chafer and extending radially inwardly downward from a radially outward level higher than the upper end of the turnup portion so as to overlappedly cover the upper end thereof and one end of the main chafer, said auxiliary chafer composed of at least two cord layers covering the outside of said main chafer, among which at least one cord layer being an outer cord layer wound along the turnup region toward the inside of the tire, and at least one cord layer arranged along the axial inside of the turnup portion as an inner cord layer and the auxiliary chafer has a triangular truss structure using a nodal point between the cord layers as a vertex that cords of at least two cord layers among said cord layers of said auxiliary chafers arranged at inclination angles of 65°-90° and 35°-55° with respect to the meridional plane of the tire, respectively, and cords of the remaining cord layer of said auxiliary chafer are arranged at an inclination angle of -50°˜-70° with respect to the meridional plane.