A vulcanizable rubber composition is presented that comprises an 
elastomer; a reinforcing filler selected from silica, 
carbon black, and mixtures thereof, a cure agent; and an amino alkoxy-modified 
silsesquioxane (AMS) comprising one or more compounds selected from the group consisting of an amino AMS, an amino / mercaptan co-AMS, an amino / blocked mercaptan co-AMS, mixtures thereof, and weak acid-neutralized 
solid and aqueous solutions thereof. Addition of such compounds to the rubber composition provides improved dynamic viscoelastic and mechanical properties of the vulcanized rubber compound and predict that tire components, especially 
tread stocks, will provide tires having improved 
snow traction, lower 
rolling resistance but equal wet traction, increased rebound, decreased 
hysteresis, and a general improvement in tire performance.