Pneumatic radial tire for heavy load vehicles including improved bead portion reinforcing construction

A pneumatic radial tire for heavy load vehicles including an improved bead portion reinforcing construction, comprising;

• at least one carcass ply wound around a bead core from the inside toward the outside thereof to form a turn-up region and composed of radially or semi-radially arranged cords, a rubber stiffener interposed between the carcass ply and the turn-up region thereof and substantially triangular in section, said rubber stiffener extending from the bead core outwardly in the radial direction of the tire, a strengthening layer arranged along the turn-up region of the carcass ply and composed of at least one metal cord layer, and a reinforcing layer surrounding both the strengthening layer and the turn-up region of the carcass ply composed of at least two organic fiber cord layers, the cords of one layer crossing with the cords of the other layer, said reinforcing layer extending continuously from a height which is higher than both the outer upper end of the strengthening layer in the radial direction and the upper end of the turn-up region of the carcass ply to the inner surface of the carcass ply, said cords of the reinforcing layer extending along the outside of the carcass ply and are inclined on a circle formed by the upper end of the turn-up region of the carcass ply at an angle of 50.degree. to 70.degree. with respect to the radial plane of the tire, said cords of the reinforcing layer have an air gap ratio .delta. to 38% to 60% measured at a region where they cross with a line tangent to a curved surface of a rim flange and extending in parallel with the rotary axis of the tire and given by:
• ##EQU4## where, b is a distance between the two midlines of two adjacent cords, measured perpendicular to the cords, and c is a cord diameter.