The invention provides a sulfur vulcanizable silica-reinforced elastomeric compound having improved tensile mechanical and dynamic viscoelastic properties. The compounds are formed by mixing an elastomer optionally having an alkoxysilane terminal group, with silica in the presence of an alkyl alkoxysilane and a blocked mercaptosilane. In particular, the mercaptosilane moiety of the blocked mercaptosilane and the alkyl alkoxysilane are present in a weight ratio of about 0.001:1 to about 0.20:1. Preferably, the blocked mercaptosilane and the alkyl alkoxysilane are compounded with the elastomer and the silica at high temperature to facilitate the silica-silane reaction. A deblocking agent is added at any desired mixing stage, optionally with the cure package, to allow binding of the mercaptosilane to the polymer.