Abstract: A bicycle having a crank assembly for driving the sprocket and chain assembly of the bicycle. The crank assembly includes a hub mounted to the frame of the bicycle so as to be rotatable at least in a direction of forward rotation. The hub is connected to a front sprocket, and two effort arm assemblies are connected to the hub. Each effort arm assembly has an effort arm. The effort arms extend outwardly substantially perpendicular to the axis of rotation of the hub, and substantially opposite to each other. Each effort arm assembly further includes an angle pedal arm. An angle pedal arm is connected to an end of the effort arm distal to the hub. Each angle pedal arm makes an angle of between about 0 and 90 degrees with the corresponding effort arm. A pedal is provided on each pedal arm, such that the pedal arm positions the pedal substantially behind the effort arm relative to the direction of forward rotation of the crank assembly. A crank assembly to modify existing bicycles is also disclosed.