A stem includes a stem body, one of the extremities of which includes element for attaching a handlebar, the opposite extremity including two parallel arms connected to a pivot tube by an articulation associated with clamping element which immobilize the stem in a chosen position. The clamping element includes a pair of frustoconical bodies connected to the extremities of the arms. The frustoconical bodies are received in housings of complementary shape. The frustoconical bodies are connected by a connecting element capable of moving them closer to one another in order to clamp them in the respective housing, and of loosening them by moving them further apart one from the other so as to allow the continuous adjustment of the inclination of the handlebar. The cone angle of the frustoconical bodies possesses a sufficiently low value to permit them to be pinched inside their housings.

An adjustable handlebar riser assembly has an outer member, an inner member, a pin, a retainer member and a locking member. The inner member and the outer member have mating flat-bottom V-shaped faces. The inner member slides at least in part within the outer member. Each of the outer and inner members has at least one aperture through their flat-bottom V-shaped faces. The pin is inserted in an aperture of the outer member and in an aperture of the inner member. The retaining member is connected to the pin at one end while the locking member is connected to an opposed end of the pin. The locking member can exert a tension on the pin, pressing the outer member onto the inner member for locking these members at a selected position relative to one another.

An adjustable riser assembly for a vehicle, wherein the riser assembly comprises a hollow outer body, an inner body telescopically slidingly disposable within the outer body, and a hand operated height adjustment pin assembly structured and operable to set and retain a selectable position of the inner body and a position of the outer body relative to each other to thereby set and retain and adjustable overall length of the adjustable riser assembly.

A foldable and portable electric vehicle for the transport of a single person comprises a foldable chassis with a support plate, a folding system for folding the chassis, a front driving wheel, a rear wheel, a foldable handlebar, an integrated system of command, control, monitoring and signaling, a mechanical brake on the rear wheel, a suspension on the rear wheel and a suspension on the front wheel, and a steering column.