To obtain a tire casing rubber composition having improved hysteresis characteristics and scorching stability.

This composition is based on at least one elastomer and silica being a reinforcing filler containing a reinforcing additive, a mixture of at least one, per molecule, functionalized polyorganosiloxane compound containing at least one functional siloxy unit chemically and/or physically bondable to the surface hydroxyl part of silica particles with at least one functionalized organosilane compound having at least one functional group bondable to the polyorganosiloxane and/or the hydroxyl part of silica particles and at least another functional group bondable chemically and/or physically to the chain of the polymer and/or an in situ reaction product therebetween. It has improved hysteresis characteristics and scorch stability.