PURPOSE: To effectively prevent the occurrence of ribber wear at both side ends of a rib positioned between longitudinal grooves during a travel.

CONSTITUTION: The tread section 1 of this tire has a plurality of ribs 4 positioned between a plurality of longitudinal grooves 2 and 2 continuously ranging in a tire peripheral direction, and between the groove 2 and the grounding end of a shoulder. The rib 4 of the tread section 1 is constituted of a laminated structure of rubber layers having different strength. Also, the upper layer 9 of the rib 4 is made of hard rubber and the lower layer 10 of soft rubber. In this case, the surface thickness (h) of the upper layer 9 is between 3/9 and 4/9 of the depth H of the longitudinal groove 2, while the lower layer 10 is formed approximately in the vicinity of the bottom depth H of the groove 2. Furthermore, the hardness of the upper layer 9 is taken at 72±5 degrees, and the hardness of the lower layer 10 at 62±4 degrees, respectively as per JISA. The thickness of the side of the upper layer 9 to cover the side of the lower layer 10 and form the side wall 15 of the groove 2 is gradually reduced in a direction toward the bottom 14 of the groove 2.