Bicycle frame having an assembled-unit shell structure

A bicycle frame having a shell structure, said frame comprising two at least generally longitudinally symmetrical shells which are attached to one another along a vertical longitudinal assembly plane, each of said two shells having a horizontal longitudinal plane of symmetry, said frame having an at least generally vertical sleeve adapted to mount a front fork, a first passage adapted to mount a support insert for a seat shaft, and a first housing adapted to mount a crank gear, said sleeve and said first passage being symmetrical about said vertical longitudinal assembly plane and said first housing being perpendicular to said vertical longitudinal assembly plane, said horizontal longitudinal plane of symmetry dividing said shells between said at least generally vertical sleeve and said first passage into two symmetrical girder elements, said first passage having a central axis and said first housing having a central axis which intersects the central axis of said first passage, the central axis of said first passage being forwardly inclined relative to said horizontal longitudinal plane of symmetry such that the upper end of said first passage is forward of the lower end of said first passage, said frame additionally having a second passage which is also symmetrical about said vertical longitudinal assembly plane and which has a central axis which is rearwardly inclined relative to said horizontal longitudinal plane of symmetry such that the lower end of said first passage is forward of the upper end of said first passage, and said frame additionally having a second housing which is also perpendicular to said vertical longitudinal assembly plane, said second housing having a central axis which intersects the central axis of said second passage.