A foldable tandem bicycle employs three separate frames joined at concentric seat tubes. The frames have quick release clamps to lock the frames into an open rigid orientation. The center frame has several configurations, male one having a closed complete frame with one diagonal brace and a female one with a pair of diagonal braces to eliminate the need for a top tube.

A folding tandem bicycle includes a front body part, a rear body part, an intermediate body part connected between the front body part and the rear body part by parallel pairs of upright tubes and pairs of connecting devices, a front transmission mechanism driven by a set of pedals through a front sprocket to rotate a front flywheel and a front wheel through a cable, and a rear transmission mechanism driven by a set of pedals through a rear sprocket to rotate a rear flywheel and a rear wheel through a chain. By disconnecting either one of each pair of connecting devices, the front body part, the intermediate body part and the rear body part are allowed to be folded up and attached with one another side by side. By disconnecting the intermediate body part from the front and rear body parts, the front and rear body parts are connected into a single-seat bicycle for one rider.

The vehicle disclosed offers significant economies from both manufacturer and user standpoints, by virtue of its being embodied in two distinct sections, front and rear, that are joined by way of a detachable coupling located between the swivel sleeve which carries the front fork and the frame which carries the rear wheel, or wheels; in a preferred embodiment, the detachable coupling is of a quick-release type.

A tandem tricycle is easily constructed from standard bicycles by removing the front wheel and fork of the rear bicycle, placing an adapter on the frame of the rear bicycle, and mounting the adapter to the rear of the leading bicycle. The adapter allows the rear bicycle to tilt, to articulate, and to bend with respect to the leading bicycle. Each function is independently achieved through suitable assemblies, and the combination allows simultaneous tilting, articulating, and bending. Although described with reference to an adapter suitable for converting standard bicycles to a tandem tricycle, the invention also contemplates the manufacture of an integral tandem bicycle or tricycle having an adapter which allows tilting, articulating, and bending of the trailing section of the tandem relative to the leading section. Multisectioned velocipedes are also contemplated.

A detachable bicycle. The bicycle includes front and rear frame sections and a detachable device having a first assembly device including a lower first sleeve extended upward from a bottom bracket sleeved on a front axle of sprocket wheel. The first sleeve includes a snap member, and an upper second sleeve at a lower end of a seat tube. The second sleeve includes a mating snap member adapted to releasably couple to the snap member. The second assembly device is adjacent to the top of the seat tube. The second assembly device includes a first coupling device formed on the seat tube and a second coupling device formed at a forward end of the seat stay. The first and the second coupling devices are releasably coupled together.