Abstract: For a vehicle such as a bicycle having a frame and at least one drive wheel, a driving sprocket, and an endless chain connecting the sprocket to the drive wheel, an improved propelling mechanism having two longer than usual pedal arms pivotally mounted on either side of the frame for swinging movement over an arc of less than 180.degree., and a slip-clutch between each pedal arm and the driving sprocket. The mechanism is such as to positively raise one pedal arm as the other is depressed. Preferably, first and second arcuate toothed members are secured to the respective pedal arms, and a first gear meshes with the first toothed member. The first gear is fixedly mounted to a transverse rotary shaft on which is also fixedly mounted a second gear. The second gear meshes with a third gear which in turn meshes with the second toothed member.