provided is an apparatus comprising a rotary power source and a continuously variable transmission coupled to the rotary power source , the continuously variable transmission comprising a first pulley assembly , a second pulley assembly , and an endless power transfer element coupled about the first pulley assembly and the second pulley assembly for transferring rotary power therebetween , the first pulley assembly being of a variable diameter type for adjusting a turning ratio relative to the second pulley assembly . the first pulley assembly comprises : a first axle defining a first axis of rotation ; a first side member coupled to rotate with the first axle and formed with a plurality of first guideways ; a second side member spatially separated from the first side member , coupled to rotate freely about the first axle , and formed with a plurality of second guideways respectively corresponding to the first guideways of the first side member at a plurality of intersections arranged in a circle about the first axis of rotation ; a plurality of pulley segments configured to engage with the endless power transfer element for transferring rotary power to or from the first pulley assembly , the pulley segments coupled with the first and second guideways at the intersections so as to be arranged in the circle about the first axis of rotation , the circle defining an effective diameter of the first pulley assembly ; actuator means for changing an angular displacement of the first side member relative to the second side member about the first axis of rotation so as to cause a coordinated change in a radial displacement of the pulley segments coupled with the first and second guideways at the intersections arranged in the circle defining the effective diameter of the first pulley assembly , and thereby changing the effective diameter of the first pulley assembly ; and tensioner means for maintaining tension in the endless power transfer element .