Rubber composition and tire with ribbed tread

A rubber composition is disclosed comprising, based on parts by weight per 100 parts by weight of the tread rubber (phr), 70 to 90, phr of a first cis 1,4-polybutadiene rubber; 10 to 30 phr of natural cis 1,4-polyisopenene rubber; wherein the first cis 1,4-polybutadiene rubber has a microstructure comprising 96 to 99 percent cis 1,4-isomeric units, a number average molecular weight (Mn) in a range of from 50,000 to 300,000, and a heterogeneity index (Mw/Mn) in a range of from 2/1 to 3.5/1; 25 to 65 phr of a rubber reinforcing carbon black; 5 to 35 phr of silica together with from 1 to 10 phr of a silica coupling agent comprising a bis(3-triethoxysilylpropyl) polysulfide; and a cure package comprising sulfur and sulfur cure accelerators; wherein the sulfur cure accelerators comprise two sulfur cure accelerators comprising: N-cyclohexyl-2-benzothiazolesulfenamide as a first sulfenamide, and N-ter-butyl-2-benzothiazolesulfenamide as a second sulfenamide; wherein the ratio of the first sulfenamide to the second sulfenamide is in a range of from 0.4/1 to 4/1. Also, a tire tread comprising such a rubber composition and a respective tire is disclosed.