Abstract: A motor assisted pedal cycle (30) comprises a pair of pedals (32) connected by crank arms (1,2) to a pedal shaft (3) which is connected to a hub (7) by means of a torsion spring (5). The hub (7) carries a drive sprocket (8) for a chain (36) to connect the hub (7) to the rear wheel of the bicycle. An internal combustion engine (38) is mounted on the bicycle frame and has an output gear for meshing with a drive gear (4) provided on the hub (7). Castellated disks (9,10) are mounted on the pedal shaft (3) and hub (7), respectively, whereby relative displacement of the pedal shaft (3) and hub (7) can be detected by means of an optical sensor (11) provided at the periphery of the disks (9,10). The output of the optical sensor (11) is used to control the engine whereby starting, stopping, and throttle control of the engine is automatically controllable by the force applied to the pedals of the bicycle.