A collapsible two wheeled vehicle comprises a substantially rigid main structural frame (10) defining a head section (16), a saddle pillar mount (17) and a bottom bracket (15). A rear wheel sub-frame (22) is pivoted to the frame (10) about the bottom bracket (15), and carriers a rear wheel (23), the sub-frame (22) being arranged for movement between a folded position where the rear wheel lies within the frame, between the head section (16) and the saddle pillar mount (17), and an active position where the sub-frame projects rearwardly beyond the frame. A pedal arrangement (19, 20, 21) is journalled in the bottom bracket (15) and drives the rear wheel (23) through an endless chain (25). A front wheel carrier is journalled to the head section (16) of the frame and has an arm (30) rotatably supporting a front wheel (31), the arm (30) being pivoted to the carrier for movement between a folded position where the front wheel (31) lies adjacent the rear wheel (23) when the sub-frame is in its folded position, and an active position where the arm projects generally downwardly from the carrier. The frame (1) carriers two opposed side panels (50) which are dimensioned so that the folded rear wheel sub-frame, rear wheel, front wheel carrier, folded arm and front wheel all lie substantially wholly within the confines of the side panels, the rear and front wheels lying outside the confines of the side panels when the sub-frame and arm are in their respective active positions.