Abstract: A transmission wheel (12) is shiftable in position radially relative to a driven member such as a bicycle wheel. A driving force is imposed to the transmission wheel (12). This driving force rotates the transmission wheel (12) and the rotational force is transmitted by drive spokes (106) from the transmission wheel (12) to a hub portion of a driven member. The radial adjustment of the transmission wheel (12) relative to the driven member changes the length of a torque arm (106, 130) which in turn changes the drive speed of the driven member. The torque arm length is the radial distance between the rotational axis (40) of the driven member and the location of drive force application onto the transmission wheel (12).