A vehicle, comprising: a frame; a seat mounted to said frame; a wheel (3, 7) rotatably mounted on said frame; and at least one drive mechanism for causing rotation of said wheel (3, 7); each of said at least one drive mechanism comprising: an arm pivotally attached at first end region to said frame; a weight arranged on said arm at an opposite, second end region; a pedal attached to said weight or to the second end region of said arm, said pedal being configured such that a user of the vehicle when present in said seat can move said pedal and thus said weight and cause pivoting of said arm; a guide member including a bump and that moves in conjunction with movement of said weight, said guide member having a first end region at which said guide member is pivotally attached to said frame and a second, opposite end region which is free and said bump being between said first and second end regions; a roller attached to said arm and movable downward and upward along said guide member during pivotal movement of said arm to cause pivoting of said guide member as said roller engages with said bump of said guide member, said roller passing over said bump in its downward movement and also passing over said bump in its upward movement; and an energy transfer system that converts pivotal movement of said guide member into motive power to rotate said wheel (3, 7); and wherein the vehicle further comprises a bracket fixed to a part of the frame leading to an axle of the rear wheel, said arm having a pivot point on said bracket and pivoting relative to this pivot point such that the radial distance of said roller from the pivot point on said bracket does not change whereby with fixing of said pedal, said weight and said arm to one another and said arm to said bracket, downward movement of said pedal, caused by force exerted by the rider of the vehicle, causes downward movement of said weight and pivotal downward movement of said arm relative to the pivot point defined on said bracket and upward movement of said pedal causes upward movement of said weight and pivotal upward movement of said arm relative to the pivot point defined on said bracket. a frame; a seat mounted to said frame; a wheel (3, 7) rotatably mounted on said frame; and at least one drive mechanism for causing rotation of said wheel (3, 7); each of said at least one drive mechanism comprising: an arm pivotally attached at first end region to said frame; a weight arranged on said arm at an opposite, second end region; a pedal attached to said weight or to the second end region of said arm, said pedal being configured such that a user of the vehicle when present in said seat can move said pedal and thus said weight and cause pivoting of said arm; a guide member including a bump and that moves in conjunction with movement of said weight, said guide member having a first end region at which said guide member is pivotally attached to said frame and a second, opposite end region which is free and said bump being between said first and second end regions; a roller attached to said arm and movable downward and upward along said guide member during pivotal movement of said arm to cause pivoting of said guide member as said roller engages with said bump of said guide member, said roller passing over said bump in its downward movement and also passing over said bump in its upward movement; and an energy transfer system that converts pivotal movement of said guide member into motive power to rotate said wheel (3, 7); an arm pivotally attached at first end region to said frame; a weight arranged on said arm at an opposite, second end region; a pedal attached to said weight or to the second end region of said arm, said pedal being configured such that a user of the vehicle when present in said seat can move said pedal and thus said weight and cause pivoting of said arm; a guide member including a bump and that moves in conjunction with movement of said weight, said guide member having a first end region at which said guide member is pivotally attached to said frame and a second, opposite end region which is free and said bump being between said first and second end regions; a roller attached to said arm and movable downward and upward along said guide member during pivotal movement of said arm to cause pivoting of said guide member as said roller engages with said bump of said guide member, said roller passing over said bump in its downward movement and also passing over said bump in its upward movement; and an energy transfer system that converts pivotal movement of said guide member into motive power to rotate said wheel (3, 7); and wherein the vehicle further comprises a bracket fixed to a part of the frame leading to an axle of the rear wheel, said arm having a pivot point on said bracket and pivoting relative to this pivot point such that the radial distance of said roller from the pivot point on said bracket does not change whereby with fixing of said pedal, said weight and said arm to one another and said arm to said bracket, downward movement of said pedal, caused by force exerted by the rider of the vehicle, causes downward movement of said weight and pivotal downward movement of said arm relative to the pivot point defined on said bracket and upward movement of said pedal causes upward movement of said weight and pivotal upward movement of said arm relative to the pivot point defined on said bracket.