Tire with tread of specialized trans 1,4-polybutadiene polymer and cis 1,4-polyisoprene natural rubber

This invention relates to a tire with a tread of a natural rubber-rich rubber composition. A partial replacement of the natural rubber in the tire tread is accomplished by an inclusion of a relatively low Mooney viscosity specialized trans 1,4-polybutadiene. The tire tread rubber composition is comprised of a blend of the specialized trans 1,4-polybutadiene polymer and cis 1,4-polyisoprene natural rubber optionally together with at least one additional diene-based elastomer in which the natural rubber remains a major portion of the elastomers in the tread rubber composition. A significant aspect of the invention is a partial replacement of natural cis 1,4-polyisoprene rubber in the tread rubber composition. The specialized trans 1,4-polybutadiene polymer has a relatively low Mooney (ML1+4), 100 DEG C, viscosity within a range of 25 to 55. The specialized trans 1,4-polybutadiene polymer has a weight average molecular weight (Mw) of less than 220,000, a number average molecular weight (Mn) of less than 120,000, and a microstructure comprised of a trans 1,4- isomeric unit content in a range of from 70 to 90 percent.