in tire tread formulations , blends of rubbers having low and high glass transition temperatures have significant advantages over blends made with rubbers having intermediate glass transition temperatures . however , blends of rubbers having low and high glass transition temperatures exhibit poor processability . this invention deals with improving the processability of tire tread formulations which are made by blending rubbers having both low and high glass transition temperatures that offer ultra low rolling resistance without sacrificing rolling resistance or tread wear characteristics . this invention more specifically discloses a tire tread rubber composition which is comprised of about 60 phr to about 90 phr of a high cis - 1 , 4 - polybutadiene rubber , wherein the high cis - 1 , 4 - polybutadiene rubber has a glass transition temperature which is within the range of about − 104 ° c . to about − 80 ° c ., about 10 phr to about 40 phr of at least one additional rubbery polymer selected from the group consisting of polyisoprene rubber , polybutadiene rubber and styrene - isoprene - butadiene rubber , wherein the additional rubbery polymer has a glass transition temperature which is within the range of about − 30 ° c . to about − 10 ° c . isoprene - butadiene rubber , about 20 phr to about 60 phr of carbon black , wherein the carbon black has a dbp absorption value of at least 140 cm 3 / 100 grams and wherein the carbon black has a ctab adsorption area which is within the range of about 60 to about 90 .