A clutch means includes an immobile tube (60) disposed between a top tube (2) and a head tube (6) of a bicycle frame, with a bearing portion (20) mounted to one of the facing end portions and axially supporting the end portions, whereby the top tube (2) and the immobile tube (60) are disposed so as to be capable of relative rotation. In the outer periphery of the bearing portion (20) and the immobile tube (60) axially supported therein, pin holes (22, 62) are respectively opened. The pin holes (22, 62) are bored at positions that are centrally aligned when a front fork (4) of the bicycle is are linearly positioned.

A convertible bicycle has separable front and rear wheel units. The convertible bicycle can operate in individual or in tandem mode as a tricycle unit. The rear wheel unit has a vertical interlocking gear which can interface with a frontal interlocking gear of the frontal wheel unit. The front wheel unit of an auxiliary bicycle can be detached and the remaining rear wheel unit attached to the rear wheel unit of another bicycle in order to form a tandem tricycle.

A tandem bicycle device is provided. The device is comprised of a tandem bicycle device configured to minimize longitudinal separation between riders through a compact frame geometry incorporating a first seat and a second seat positioned in close proximity, as well as a closely spaced front crankset and rear crankset. The device has a second handlebar set connected to the frame via a pivot point allowing forward rotation of the handlebar set for active use by a second rider or retraction when not in use. The pedal system comprises two cranksets interconnected by a synchronization mechanism such as a dual-chain or timing belt system to ensure coordinated pedaling. The overall configuration reduces torsional frame flex and aerodynamic drag while improving shared rider control and engagement.

A tandem bicycle device is provided. The device is comprised of a tandem bicycle device configured to minimize longitudinal separation between riders through a compact frame geometry incorporating a first seat and a second seat positioned in close proximity, as well as a closely spaced front crankset and rear crankset. The device has a second handlebar set connected to the frame via a pivot point allowing forward rotation of the handlebar set for active use by a second rider or retraction when not in use. The pedal system comprises two cranksets interconnected by a synchronization mechanism such as a dual-chain or timing belt system to ensure coordinated pedaling. The overall configuration reduces torsional frame flex and aerodynamic drag while improving shared rider control and engagement.