| abstract |
A pneumatic tire having a circumferential tread (2) comprising an outer tread cap layer (3) and an underlying sub tread cap layer (4) is disclosed. The outer tread cap layer (3) is of a rubber composition comprising conjugated diene based elastomers comprising 20 to 80 phr of natural cis 1,4-polyisoprene rubber (NR) and 80 to 20 phr of cis 1,4-polybutadiene rubber (BR), wherein the polybutadiene rubber (BR) comprises a combination of a designated (BR1) and a specialized (BR2) cis 1,4-polybutadiene rubber. The underlying sub tread layer (4) is of a rubber composition comprising conjugated diene based elastomers comprising 40 to 60 phr of natural cis 1,4-polyisoprene rubber (NR) and 60 to 40 phr of cis 1,4-polybutadiene rubber (BR), wherein the polybutadiene rubber (BR) comprises a combination of the designated (BR1) and the specialized (BR2) cis 1,4-polybutadiene rubber. The specialized cis 1,4-polyisoprene rubber has a microstructure comprising 90 to 99 percent cis 1,4-isomeric units, a number average molecular weight (Mn) in a range of from 90,000 to 220,000 and a heterogeneity index (Mw/Mn) in a range of from 2.5/1 to 5/1. The designated 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 150,000 to 300,000 and a heterogeneity index (Mw/Mn) in a range of from 1.5/1 to 2/1. |