Abstract: Tread rubber compositions or use in automobile tires are disclosed which essentially comprise matrix rubbers and specified amounts of a selected class of low-hardness vulcanized rubbers having specified particle sizes. The matrix and vulcanized rubbers include carbon black, respectively, in amounts defined by the equation 0<X.ltoreq.Y/3 where X is the amount of carbon black present in the vulcanized rubber, and Y is the amount of carbon black in the matrix rubber, each such amount being based on the total weight of the matrix rubber. The resulting tire is rendered highly resistant to snowy and icy conditions and also to abrasive wear.

Abstract: A pnuematic tire having a cap tread and a base tread is defined in way of material as follows:(1) said cap tread is made of a rubber material in which 100 pts. wt. of rubber component comprising at least 50 pts. wt. of natural rubber and/or polyisoprene rubber, at most 50 pts. wt. of polybutadiene rubber containing at most 20% of 1,2-bonding units and at most 50 pts. wt. of styrene-butadiene copolymer rubber containing at most 30 wt % of bonded styrene is incorporated with 50 to 100 pts. wt. of carbon black and with a softener in an amount satisfying the inequality;1.1X-44<y<1.1X-30,where y is the total amount of the softener in pts. Wt.; x is the amount of carbon black in pts. wt.; and an overall solubility parameter of the softener is in the range of from 8.0 to 9.0,(2) said base tread is made of a rubber material in which 100 pts. wt. of rubber component comprising at least 60 pts. wt. of natural rubber and/or polyisoprene rubber, at most 40 pts. wt.

Abstract: A rubber composition for tire tread, comprising natural rubber and/or polyisoprene rubber and polybutadiene rubber, which polybutadiene rubber having a 1,2-bond unit content in the range of 40 to 90 mol % and having a specific functional group contained in the molecular chain thereof.

Abstract: A radial tire having an under-tread layer between a cap tread and a breaker layer is disclosed. As the material for the cap tread, a rubber composition is employed which contains 0.5 to 1.6 parts by weight of sulfur per 100 parts by weight of starting rubber components consisting of 25 to 75 parts by weight of polybutadidne rubber having 65 to 90 mol % of 1,2-bonding units and 75 to 25 parts by weight of natural rubber and/or polyisoprene rubber, and which has elongation at break of at least 330% at 100.degree. C. A rubber composition containing 1.6 to 10 parts by weight of sulfur per 100 parts by weight of rubber components is used for the under-tread layer.

Abstract: A process for preparing a rubber composition for tire treads having resilience, wet skid resistance and wear resistance well balanced with each other, by mechanically mixing a specific amount in total of a halogenated butyl rubber, natural rubber or a polyisoprene rubber and a polybutadiene rubber with a specific amount of carbon black and with other additives in the first mixing step and then mechanically mixing the resulting mixture with the remainder of the rubber ingredients and carbon black in the second mixing step thereby to obtain the rubber composition.

Abstract: A rubber composition for tire treads having improved rolling resistance and wet road braking performance, comprising (I) a chlorinated butyl rubber and/or a brominated butyl rubber, (II) natural rubber and/or a polyisoprene rubber and, if desired, (III) a polybutadiene rubber in specific blending ratios.

Abstract: A process for preparing a tire tread rubber composition having improved rolling resistance and wet skid resistance comprising [I] 100 parts by weight of a rubber material composed of 25 to 75% by weight of substantially amorphous polybutadiene having a 1,2-bond unit content of 65 to 90 mole % and a Mooney viscosity (ML.sub.1+4, 100.degree. C.) of 20 to 100 and 75 to 25% by weight of natural rubber and/or cis-1,4-polyisoprene, and [II] 40 to 70 parts by weight of carbon black, said process comprising (1) mechanically compounding 40 to 60 parts by weight of the rubber material [I] with 40 to 70 parts by weight of carbon black [II], and then (2) adding to the resulting mixture the rubber material [I] in an amount sufficient to adjust the amount of the carbon black [II] to 40 to 70 parts by weight per 100 parts by weight of the rubber material [I] and mechanically compounding them.

Abstract: A tread composition for low rolling resistance tires, comprising 100 parts by weight of styrene-butadiene rubber or a styrene-butadiene rubber-based rubber blend and 3.2-5.0 parts by weight of sulphur.