The present invention relates to a heterogeneous silica/carbon black-filled rubber compound and a process for making the same. The process comprises (a) intimately dispersing substantially all of the silica filler in a first rubber to form a silica-filled compound; (b) separately intimately dispersing the majority of carbon black in a second rubber, which is different from said first rubber, to form a carbon black-filled compound; and (c) mixing said silica-filled compound with said carbon black-filled compound to form a heterogeneous silica/carbon black-filled rubber compound.