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, unisex one having a closed complete frame with one diagonal brace and a second one with a pair of diagonal braces to eliminate the need for a top tube. A third embodiment employs in-line intermediate members.

Transmission assembly, particularly for bicycles or the like, having an inside box-like body, a first chain ring associated with a pedal crank shaft and connected to a pinion by a first chain, and a second chain ring associated with a second shaft and rotating rigidly with said pinion. A second chain is associated with the second chain ring and is adapted to transmit the motion to a gearshift assembly constituted by a plurality of gears that can be selectively associated with the second chain by a derailleur. The gearshift assembly is rigidly coupled to a hub that supports a wheel in a cantilevered manner outside the box-like body.

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.

A foldable bicycle includes a frame. A first foldable device is connected to a top tube of the frame so as to fold a front wheel together with a head tube and a handlebar backward at the first foldable device such that the front and rear wheels are located parallel with each other. At least one assistant wheel is connected to a lower end of a down tube so that the at least one assistant wheel cooperates with the front and rear wheels to form a stable triangle support arrangement and the foldable bicycle can be easily moved by the at least one assistant wheel cooperating with the front and rear wheels. A carry rack is located above the rear wheel, which can be positioned by engaging pivot rods of the carry rack with engaging members on two support rods connected to a hub of the front wheel.

A foldable bicycle frame comprises a front frame made up of a head tube, a top tube and a down tube, and a rear frame made up of a seat tube, a bottom bracket tube, a seat stay and a chain stay. The top tube is provided at the rear end thereof with a connection tube to receive therein a seat post. The bottom bracket tube is provided at the center of the front end thereof with an extension tube which faces the front wheel and is pivoted at the front end thereof to the bottom end of the down tube. The front frame and the rear frame are fastened together by means of the seat post which is inserted into the connection tube and the seat tube. The front frame and the rear frame are rotatable in relation to each other when the seat post is pulled out of the seat tube.