To mitigate setting conditions for reduction of rolling resistance and improvement of steering stability by making a tread part into a two-layer structure of a cap tread layer and under-tread layer.
An under tread layer 4b is composed of a center area in a range of 30 to 70% of a width of a belt layer 5a and 0.5 to 2.0 mm from the belt layer 5b in a tire diametral direction, and a shoulder area continuing from the center area and in a range extended outside from both ends of the belt layer 5a at a maximum 30 mm on one side and width of 1.0 to 5.0 mm, made of mutually different rubber compositions. A rubber layer 4b1 with a JIS-A hardness in a range of 65 to 80 degrees and a mixed amount of softening agent ten parts by weight or more lesser than a cap tread layer 4a is arranged in the center area. A rubber layer 4b2 with a JIS-A hardness in a range of 50 to 70 degrees and a mixed amount of softening agent ten parts by weight or more lesser than the cap tread layer 4a is arranged in the shoulder area. A ratio of a loss tangent of the rubber layer 4b2 of the shoulder area to a loss tangent of the rubber layer 4b1 is two thirds or less.
AMINO NAOYA
TAKASUGI MOTOHIDE
