Abstract: A rubber composition prepared by compounding 0.05 to 20 parts by weight of at least one selected from substituted hydrazide compounds represented by the following Formulas (I) to (IV) per 100 parts by weight of a rubber component comprising at least one rubber selected from the group consisting of natural rubber and synthetic rubber, and a pneumatic tire using the same: wherein A represents one selected from the group consisting of an aromatic group which may have a substituent, a hydantoin ring which may have a substituent, and a saturated or unsaturated linear hydrocarbon having 1 to 18 carbon atoms; Y represents hydrogen, an amino group, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an alkenyl group, an aromatic group, a pyridyl group or hydrazino group; and R1 to R11 each represent hydrogen, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group or an aromatic group.

Abstract: A pneumatic tire for heavy loads having a rubber composition for a tread rubber for a construction vehicle or the like, containing carbon black having a nitrogen adsorption specific surface area of 100 to 160 m.sup.2 /g, and an oil (dibutyl phthalate) absorption amount (DBP) of 80 to 130 ml/100 g, and silica having a nitrogen adsorption specific surface area of 210 to 260 m.sup.2 /g, and an oil absorption amount of 200 to 260 ml/100 g, by a total content of 40 to 70 parts by weight, in 100 parts by weight of isoprene rubber material, wherein the rubber composition contains 3 to 15 parts by weight of the total content. Further, the rubber composition contains 30 to 50 parts by weight of carbon black having a nitrogen adsorption specific surface area of 130 to 180 m.sup.2 /g, and an oil (dibutyl phthalate) absorption amount (DBP) of 80 to 120 ml/100 g, and 5 to 15 parts by weight of silica having a nitrogen adsorption specific surface area of 170 m.sup.2 /g or more, and 2.

Abstract: A heavy duty vehicle pneumatic tire comprising a tread, wherein the tread is composed of a diene-based rubber composition, and crystalline syndiotactic-1,2-polybutadiene is incorporated into said rubber composition in an amount of 5 to 60 parts by weight relative to 100 parts by weight of a diene-based rubber component of the rubber composition. The syndiotactic 1,2-polybutadiene has a melting point of 130.degree. to 170.degree. C., an average particle diameter of not more than 100 .mu.m, and a ratio of a major axis to a minor axis (L/D) being not more than 3. The content of 1,2-structural units in the syndiotactic-1,2 polybutadiene is not less than 75% by weight, and a syndiotacticity of the 1,2-structural units is not less than 75%.