Pneumatic radial tire

A heavy-duty pneumatic radial tire comprising:

• a main belt layer provided in the tread portion, and including two belt layers in which steel cords of the two belt layers intersect each other, wherein outer peripheral end portions in a tire width-wise direction of a radially outermost of the two belt layers are inclined toward an outer peripheral edge of the tire, and outer peripheral end portions in a tire width-wise direction of a radially innermost of the two belt layers are flat;
• and
• at least one circumferential-direction reinforcement layer provided in the tread portion, the reinforcement layer being formed from a single layer of steel cords disposed substantially in a tire circumferential direction, wherein each of the steel cords is unbent in a tire axial direction, and wherein
• the ratio Wo/Wm of the width Wo of the circumferential-direction reinforcement layer to the maximum width Wm of the main belt layer is 0.5 to 0.9, and
• the ratio Ee/Ec of the reinforcement-cord elastic modulus Ee of the steel cords in the edge portions of the circumferential-direction reinforcement layer to the reinforcement-cord elastic modulus Ec of the steel cords in the center portion of the circumferential-direction reinforcement layer is not less than (0.85−0.5 Wo/Wm) and not more than 0.8,
• wherein the tire has a maximum width of not less than 350 mm and an aspect ratio of not more than 60% when the tire is inflated with an air pressure corresponding to the maximum load capacity defined by JATMA, such that the tire is used in place of conventional dual tires,
• wherein the circumferential-direction reinforcement layer is disposed in one of a portion between the two belt layers of the main belt layer and a portion on the innermost periphery of the main belt layer, and
• wherein a single auxiliary belt layer which is formed of steel cords and narrower than the main belt layer is disposed radially inward of the main belt layer such that the auxiliary belt layer covers at least a portion of the tire including, an axially central portion of the tire, and the main belt layer completely covers the auxiliary belt layer, the steel cords of the auxiliary belt layer having an inclination angle greater than inclination angles of the two belt layers forming the main belt layer.