An inverted tooth chain drive system comprising: a sprocket supported for rotation about an axis of rotation and comprising a plurality of teeth (260,280) defined relative to respective tooth centers, said tooth centers spaced evenly in a circumferential arrangement about said axis of rotation, each of said plurality of teeth comprising an engaging flank (262,282) and a disengaging flank, wherein at least some of said teeth are standard teeth and other ones of said teeth are flank-relieved teeth, and said plurality of teeth are separated from each other by respective root surfaces (265,285), with the respective root surfaces adjacent and leading the flank-relieved teeth being raised root surfaces that are located radially outward with respect to the respective root surfaces adjacent and leading the standard teeth; said engaging flanks of said flank-relieved teeth are negatively offset relative to their respective tooth centers as compared to said engaging flanks of said standard teeth; an inverted tooth chain engaged with the sprocket; said inverted tooth chain drive system characterized in that: said inverted tooth chain comprises a plurality of rows (230a, 230b,..., 230n) of links each structured for inside flank engagement with the sprocket, with leading inside flanks of each row projecting outwardly relative to the trailing outside flanks of a preceding row; initial meshing engagement between each one of said sprocket teeth (260,280) and said chain includes, for both said standard teeth and said flank-relieved teeth, initial contact between the tooth engaging flank (262,282) and the leading inside flanks of a meshing chain row, followed by separation of said leading inside flanks of the meshing chain row from the tooth engaging flank; and, when said inverted tooth chain fully meshes with one of said flank-relieved teeth, both said leading inside flanks and said trailing outside flanks of said chain are spaced from the engaging flank of the flank-relieved tooth and toes of said chain make root contact with said raised root surface adjacent and leading said flank-relieved tooth. a sprocket supported for rotation about an axis of rotation and comprising a plurality of teeth (260,280) defined relative to respective tooth centers, said tooth centers spaced evenly in a circumferential arrangement about said axis of rotation, each of said plurality of teeth comprising an engaging flank (262,282) and a disengaging flank, wherein at least some of said teeth are standard teeth and other ones of said teeth are flank-relieved teeth, and said plurality of teeth are separated from each other by respective root surfaces (265,285), with the respective root surfaces adjacent and leading the flank-relieved teeth being raised root surfaces that are located radially outward with respect to the respective root surfaces adjacent and leading the standard teeth; said engaging flanks of said flank-relieved teeth are negatively offset relative to their respective tooth centers as compared to said engaging flanks of said standard teeth; an inverted tooth chain engaged with the sprocket; said inverted tooth chain drive system characterized in that: said inverted tooth chain comprises a plurality of rows (230a, 230b,..., 230n) of links each structured for inside flank engagement with the sprocket, with leading inside flanks of each row projecting outwardly relative to the trailing outside flanks of a preceding row; initial meshing engagement between each one of said sprocket teeth (260,280) and said chain includes, for both said standard teeth and said flank-relieved teeth, initial contact between the tooth engaging flank (262,282) and the leading inside flanks of a meshing chain row, followed by separation of said leading inside flanks of the meshing chain row from the tooth engaging flank; and, when said inverted tooth chain fully meshes with one of said flank-relieved teeth, both said leading inside flanks and said trailing outside flanks of said chain are spaced from the engaging flank of the flank-relieved tooth and toes of said chain make root contact with said raised root surface adjacent and leading said flank-relieved tooth. said inverted tooth chain comprises a plurality of rows (230a, 230b,..., 230n) of links each structured for inside flank engagement with the sprocket, with leading inside flanks of each row projecting outwardly relative to the trailing outside flanks of a preceding row; initial meshing engagement between each one of said sprocket teeth (260,280) and said chain includes, for both said standard teeth and said flank-relieved teeth, initial contact between the tooth engaging flank (262,282) and the leading inside flanks of a meshing chain row, followed by separation of said leading inside flanks of the meshing chain row from the tooth engaging flank; and, when said inverted tooth chain fully meshes with one of said flank-relieved teeth, both said leading inside flanks and said trailing outside flanks of said chain are spaced from the engaging flank of the flank-relieved tooth and toes of said chain make root contact with said raised root surface adjacent and leading said flank-relieved tooth.