Patent ID: 6939920

Claim:
In a sidewall compound comprising a mix of synthetic rubber, natural rubber, carbon black, an antidegradant and processing aids, which mixture is cured with a curative package, the improvement comprising, natural rubber present in a minor proportion by weight relative to all the rubber in the compound; synthetic rubber of cis-1,4-polybutadiene present in the range from 55 phr to 7phr, the cis-1,4-polybutadiene having a cis-content of at least 90%, a polydispersity in the range from about 3 to 5, a number average molecular weight Mn in the range from 100,000 to 150,000 and a degree of branching in the range from 2 to 3.5; wherein, the sidewall compound has an elongation at break higher than that of a sidewall compound made with a cis-1,4-polybutadiene having a polydispersity less than 3.