Patent ID: 8772374

Claim:
A process of preparing a rubber composition is provided which comprises the steps of: (A) blending a rubber composition, in at least one preliminary blending step, comprised of: (1) 100 phr of at least one conjugated diene-based elastomer, (2) from about 25 to about 120 phr of reinforcing filler comprised of pretreated silica, and (3) from about 0.3 to about 8 phr of a combination of two bis(3-triethoxysilylpropyl) polysulfides comprised of: (a) a first bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to about 2.4 connecting sulfur atoms in its polysulfidic bridge, and (b) a second bis(3-triethoxysilylpropyl) polysulfide having an average of from 3.4 to about 3.8 connecting sulfur atoms in its polysulfidic bridge, wherein a ratio in a range of from about 20/80 to about 80/20 of said first and second bis(3-triethoxysilylpropyl) polysulfides is used, followed by: (B) blending, in a subsequent blending step, with the rubber composition from said preliminary blending step(s) a sulfur curative comprised of elemental sulfur; wherein said pre-treated silica is a precipitated silica treated with a silica coupling agent to form a composite of precipitated silica/coupling agent prior to addition to said rubber composition, wherein said silica coupling agent for said composite is comprised of a siloxyorganomercaptosilane.