A partially sulfur pre-vulcanized rubber composition comprised of, based on 100 parts by weight of elastomer, (A) at least one solid diene-based elastomer selected from homopolymers and copolymers of conjugated diene and copolymers of at least one conjugated diene with a vinyl aromatic compound selected from styrene and alpha-methylstyrene, (B) about 3 to about 15 phr of liquid conjugated diene polymer having a molecular weight in a range of about 1,000 to about 40,000, (C) from about 45 to about 65 phr of reinforcing filler selected from amorphous silica, amorphous aluminosilicate, and modified carbon black;
- wherein said amorphous silica, aluminosilicate and modified carbon black have silanol groups on the surface thereof, wherein said modified carbon black is prepared by treating carbon black with an alkoxy or organoalkoxy silane or by co-fuming carbon black and silica, and, wherein said reinforcing filler contains from about 60 to about 100 weight percent of at least one of said amorphous silica and aluminosilicate and (D) a coupling agent having a moiety reactive with said silanol groups on the surface of the said amorphous silica, aluminosilicate and modified carbon black and another moiety interactive with at least one of said diene-based elastomers;
- wherein said rubber composition is pre-sulfur vulcanized to about 20 to about 60 percent of its T90 vulcanization state.