A process of preparing a rubber composition, the process comprising the steps: blending a rubber composition, in at least one preliminary blending step, the rubber composition comprising: 100 phr of at least one conjugated diene-based elastomer, from 25 to 120 phr of a reinforcing filler comprising a pretreated silica, and from 0.3 to 8 phr of a combination of two bis(3-triethoxysilylpropyl) polysulfides comprising: (a) a first bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 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 3.8 connecting sulfur atoms in its polysulfidic bridge; wherein a ratio in a range of from 20/80 to 80/20 of said first and second bis(3-triethoxysilylpropyl) polysulfides is used. blending, in a subsequent blending step, with the rubber composition from said preliminary blending step(s) a sulfur curative comprising elemental sulfur; wherein said pretreated 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 comprises: an alkoxyorganomercaptosilane, or combination of an alkoxyorganomercaptosilane and at least one of alkylsilane and alkoxysilane. blending a rubber composition, in at least one preliminary blending step, the rubber composition comprising: 100 phr of at least one conjugated diene-based elastomer, from 25 to 120 phr of a reinforcing filler comprising a pretreated silica, and from 0.3 to 8 phr of a combination of two bis(3-triethoxysilylpropyl) polysulfides comprising: (a) a first bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 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 3.8 connecting sulfur atoms in its polysulfidic bridge; wherein a ratio in a range of from 20/80 to 80/20 of said first and second bis(3-triethoxysilylpropyl) polysulfides is used. 100 phr of at least one conjugated diene-based elastomer, from 25 to 120 phr of a reinforcing filler comprising a pretreated silica, and from 0.3 to 8 phr of a combination of two bis(3-triethoxysilylpropyl) polysulfides comprising: (a) a first bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 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 3.8 connecting sulfur atoms in its polysulfidic bridge; (a) a first bis(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 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 3.8 connecting sulfur atoms in its polysulfidic bridge; blending, in a subsequent blending step, with the rubber composition from said preliminary blending step(s) a sulfur curative comprising elemental sulfur; wherein said pretreated 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 comprises: an alkoxyorganomercaptosilane, or combination of an alkoxyorganomercaptosilane and at least one of alkylsilane and alkoxysilane. an alkoxyorganomercaptosilane, or combination of an alkoxyorganomercaptosilane and at least one of alkylsilane and alkoxysilane.