A tire is provided having a circumferential tread of a diene-based rubber
composition reinforced with a silica-containing carbon black which
contains domains of silica on its surface prepared by extended reactive
mixing of said silica-containing carbon black with a coupling agent
together with at least one elastomer. Said silica-containing carbon black
is a carbon black which contains silica domains on its surface and said
silica contains hydroxyl groups (e.g. silanol groups) on its surface,
wherein said silica domains cover at least 50 percent of the carbon black
surface. Said coupling agent is a bis(3-triethoxysilylpropyl) polysulfide
having an average of from 2 to 4, alternately a more limited average of
from 2 to 3 or from 2 to 2.6, connecting sulfur atoms in its polysulfidic
bridge. In one aspect of the invention, it is preferred that said
coupling agent is exclusive of a bis(3-trialkoxysilylalkyl) polysulfide
having an average of greater than 3.5 sulfur atoms in its polysulfidic
bridge.