A heavy duty pneumatic radial tire in which three types of durability, the durability of a folded-back part of a carcass, the durability of a rubber layer of the carcass, and the durability of carcasscords against breakage, are enhanced. The steel radial carcass (12) is constructed from a main carcass part (12M) and folded-back parts (12E), and the tire is assembled to a standard rim (20). If P1is a position on the outer surface of the tire away in the radial direction from the center axis of the tire by (R + 1.18 x Hf), P2 is a position on the outer surface away in the radial direction fromthe center axis of the tire by (R + 0.81 x Hf), T1 and T2 are respectively the intersections between a folded-back part (12E) and normal lines drawn from P1 and P2 to the main carcass part (12M), andM1 and M2 are respectively the intersections between the main carcass part (12M) and the normal lines, the positions of T1, T2, M1, and M2 satisfy a predetermined relative positional relationship.