The plasticity of a tread composition may advantageously be increased by incorporating, for example, a relatively small amount of an ultra high molecular weight polyethylene ("UHMWPE"). A tread cap composition, in accordance with the principles of the invention, may be a composition resulting from the combination of components including: a sulfur-vulcanizable elastomer containing olefinic unsaturation; a reinforcing filler; a mineral oil softener; a silane coupling agent; and an ultra high molecular weight polyethylene ("UHMWPE").