A composite bicycle frame comprises a diagonal down tube connected via a bottom bracket to a saddle tube and two rear forks, back stays, and a cross-bar between the top of the saddle tube and the steering tube. The diagonal tube, saddle tube, and rear forks form a first sub-assembly which is molded in one piece, while the cross-bar, saddle joint and upper end of the steering tube form a second sub-assembly, also in one piece, and the two sub-assemblies are joined with adhesive.

An improved frame involves two main principles which contribute to a superior bicycle frame. The first principle involves the use of a tear drop cross sectionally shaped down tube which is oriented with the small radius side facing forward and down. This orientation of the tube, for a given size of bicycle frame yields an unexpectedly high force to failure characteristic. In the case of a forward shock as by hitting a pothole, rock, or log, the resulting frame will be much more resistant to damage. Secondly, the preferred embodiment of the frame includes three sections, including a teardrop section, a transition section in which the teardrop shape transitions to a round shape, and a length of straight tube. The transition to a round shape, with or without a length of constant circular round shape adds rigidity to the bottom of the frame to provide provide increased lateral support.

A bicycle frame part made via a process that includes the steps of placing a one-piece metallic tube blank in a die; hydraulically forming the tube blank by introducing a hydraulic pressure into the tube blank to deform and expand the tube blank so as to form at least one expanded wall part projecting from the tube blank along a direction different from the direction of extension of the tube blank; and machining the expanded wall part to form a connection tube. A bicycle frame includes a plurality of frame parts connected to each other. At least one of the frame parts is formed via the aforementioned process, and includes a tube body and at least one connection tube projecting from the tube body in a direction different from the direction of extension of the tube body.

A body frame of a two-wheeled vehicle. The body frame typically includes a head pipe to which a steering shaft extending substantially vertically is rotatably mounted. The head pipe includes an upper head pipe and a lower head pipe that are configured to be molded and to be coupled to each other. The upper head pipe includes an upper tubular portion into which the steering shaft is inserted and a main frame tongue portion that is configured to extend rearward from the upper tubular portion and is configured to support a front portion of the main frame from above. The lower head pipe includes a lower tubular portion into which the steering shaft is inserted and a down tube tongue portion that is configured to extend downward from the lower tubular portion and to support an upper portion of the down tube from forward.

A method for making a bicycle frame part includes the steps of preparing a malleable tubular blank that has an outer surface and that is made from an alloy selected from the group consisting of Al--Mg--Sc alloy, Al--Mg--Zr alloy, and Al--Mg--Li--Zr alloy; placing the tubular blank in a mold such that the tubular blank is surrounded by an inner surface of the mold; heating the tubular blank to a working temperature ranging from 200 to 500.degree. C; and injecting a high-pressure fluid into the tubular blank so as to permit expansion and permanent deformation of the tubular blank in the mold to an extent that the outer surface of the expanded tube abuts against and conforms to the inner surface of the mold.