Abstract: Heavy duty pneumatic radial tire which has the feature as follows: a pair of bead cores; a carcass ply which is composed of steel cords being turned up around the bead core from the inside toward the outside and disposed with respect to the radial direction; a belt layer whose cords are disposed at a comparative low angle with respect to the equatorial line of the tire and a steel cord reinforcing layer disposed adjacent to the outside of the turned up portion of the carcass ply, the height ho of the said turned up portion from the bead base portion is within a range of between 55 mm and 80 mm.The rubber thickness t which is between the carcass ply itself and its turned up portion, is at a certain height h from the bead base portion, t/h decreases gradually in inverse proportion to values of h/h0 within the range of 0.3.ltoreq.h/h0.ltoreq.0.5 or 0.3.ltoreq.h/h0.ltoreq.0.8, and takes an approximate constant value from 0.1 to 0.25 within the range of 1.0.ltoreq.h/h0>0.5 or 1.0.ltoreq.h/h0>0.8.

Abstract: A heavy duty pneumatic radial tire is disclosed, which comprises a carcass composed of at least one rubberized ply containing cords arranged substantially in a radial plane of the tire and a belt superimposed about a crown portion of the carcass just beneath a tread and composed of at least three rubberized belt plies. In this tire, metal cords of a first belt ply nearest to the carcass among the above belt plies are arranged at an angle of 25.degree.-50.degree. without crossing with metal cords of a second belt ply near the carcass next to the first belt ply with respect to a central circumferential line of the tire, and metal cords of the second belt ply and a third belt ply near the carcass next to the second belt ply, a tensile strength of each of which being 1.5-2 times that of the metal cord of the first belt ply, are arranged at an angle of 10.degree.-30.degree.