Abstract: An improved variable radius chain or belt transmission is provided for bicycle, motorcycle, automobile, industrial, household and consumer product uses. It delivers power and shifts under power through a continuously variable range of ratios. Alternative means are disclosed: for properly engaging the chain or belt regardless of drive radius; for handing off the workload of the chain or belt even while the drive's effective radius is changing; for minimizing the force required to expand a drive under chain or belt; for supporting the chain or belt attachment points in radially variable manner; for circumferentially bridging the spans between radial attachment points; for coordinating the radial movement of the attachment points within one drive; for actuating up-shifting or down-shifting processes in forward or reverse; and for simultaneously varying the effective radii of input and output drives in coordinated fashion.