Patent ID: 7956146

Claim:
A pneumatic rubber tire having a circumferential rubber tread wherein said tread is a rubber composition exclusive of cis 1,4-polyisoprene rubber and comprised of, based on parts by weight per 100 parts by weight of the tread rubber (phr), (A) 100 phr of cis 1,4-polybutadiene rubber comprised of: (1) specialized cis 1,4-polybutadiene rubber, having a microstructure comprised of about 96 to about 99 percent cis 1,4-isomeric units, about 0.1 to about 1 percent trans 1,4-isomeric units and from about 1 to about 3 vinyl 1,2-isomeric units; a number average molecular weight (Mn) in a range of from about 90,000 to about 130,000 and a heterogeneity index (Mw/Mn) in a range of from about 2.5/1 to about 5/1, wherein said specialized cis 1,4-polybutadiene rubber is the product of polymerization of 1,3-butadiene monomer in an organic solvent in the presence of a catalyst composed of nickel octoate, triisobutylaluminum, hydrogen fluoride and parastyrenated diphenylamine, or (2) said specialized cis 1,4-polybutadiene rubber and up to 50 phr of designated cis 1,4-polybutadiene rubber having a microstructure comprised of about 96 to about 99 percent cis 1,4-isomeric units, a number average molecular weight (Mn) in a range of from about 150,000 to about 200,000 and a heterogeneity index (Mw/Mn) in a range of from about 1.5/1 to about 2/1, wherein said designated cis 1,4-polybutadiene rubber is the product of polymerization of 1,3-butadiene monomer in an organic solvent in the presence of a neodymium catalyst; (B) about 40 to about 110 phr of reinforcing filler wherein said reinforcing filler is a combination of rubber reinforcing carbon black and synthetic amorphous silica (precipitated silica) comprised of: (1) about 20 to about 60 phr of rubber reinforcing carbon black, and (2) about 10 to about 80 phr of precipitated silica; (C) coupling agent having a moiety reactive with hydroxyl groups on said precipitated silica and another different moiety interactive with carbon-to-carbon double bonds of said cis 1,4-polybutadiene rubber.