A dual seat adaptor for a bicycle that allows a second person to ride on a conventional bicycle. Both a front seat post and a rear seat post are telescopically received in the respective front and rear seat post sleeves that are the most important structure of the dual seat adaptor. The front seat post sleeve is telescopically received in the top end of the seat supporting tube of the conventional bicycle.

This invention relates to an improvement in men's and ladies' folding and tandem bicycles. The improvement provides commonality of structural and mechanical means and commonality of configuration components between a men's and ladies style bicycle, and tandem bicycles. This invention provides a bicycle with alternative men's and ladies' model structural means. It permits elimination of the top horizontal bar of the folding bicycle frame, allowing construction of a ladies' style folding bicycle, which folds on three axes with exclusive structural support means in the lower member or members fixedly secured to a vertical structural spreader bar in the rear of the bicycle frame. The said vertical bar provides vertical adjustable seat support means for the rider, with the seat remaining in proper forward adjustment during folding and unfolding of the bicycle. The improvement expands the capability of bicycle folding means into ladies' model configuration and tandem rider model configurations. There is a commonality of construction in a men's, ladies', and tandem model configurations. A detent is disclosed to manually release and retain the articulated latches when they are locked, thereby avoiding inadvertant release when the bicycle is ridden. An eccentric adjusts out the looseness in the folding joints to provide adjustment for manufacturing tolerances and normal wear. Also disclosed is a tandem style bicycle the size of a single rider model, except that it has provisions for a tandem seat and a tandem set of pedals with the pedals mounted forward of the rear wheel center axle.

A close-coupled tandem bicycle is described with a shorter wheelbase than a standard tandem bicycle and with the front and rear riders positioned closer together for easier communication and interaction between them. Two pedal cranks drive the rear wheel through a sprocket-and-chain drive. Both the front and rear passenger can steer the bicycle. A main handlebar with long handgrips extends rearward within easy reach of the rear passenger. A secondary handlebar attaches to the main handlebar and extends in front of it for use by the front passenger. The height and forward extension of the secondary handlebar is adjustable independently of the main handlebar so that both passengers can adjust the seat and the handlebars to their liking. The tiding positions can be adjusted to allow two riders of different sizes, such as a child and an adult, to ride together in comfort. The close-coupled seating arrangement gives a child riding in the front seat a greater sense of safety than the head-to-tail arrangement of standard tandems. A blind or handicapped passenger can also ride in the front or rear position and truly participate in steering and controlling the bicycle with the increased sense of security of having another rider in close proximity. The fore-and-aft adjustability of the riding positions also allows two riders to move very close together so that they can ride in a closer, almost intimate, riding position perfect for taking romantic bicycle rides together.

A drive system for a tandem bicycle (10) to allow a captain or a stoker to pedal independently of one another. A unidirectional bearing, e.g., a freewheel assembly (24) is incorporated in a captain crank assembly (20), a stoker crank assembly (100), or both assemblies. In the preferred embodiment of the captain crank assembly, a first adapter plate (36) and a second adapter plate (38) attach the freewheel assembly to a chainring (34). In the preferred embodiment of the stoker crank assembly, a first adapter plate (102) and a second adapter plate (104) attach the freewheel assembly to four chainrings (114, 128, 130, 134). The captain crank assembly is coupled to the stoker crank assembly by a single chain (12), and the stoker crank assembly is coupled to a rear hub (18) of the bicycle by a single chain (14). When the freewheel assembly is incorporated in both the captain crank assembly and the stoker crank assembly, either rider may stop pedaling while the other rider continues to pedal forward.

A drive train for a tandem bicycle, in which the riders are positioned one behind the other, comprising a transverse intermediate shaft mounted on the bottom tube of a tandem bicycle between the two standard bottom brackets for the respective riders. Chains driven by the respective riders drive separate sprockets, each having an independent free-wheel driving connections to the intermediate shaft and being smaller than the respective chainring which drives it. The intermediate shaft has one or more relatively small chain rings to drive the rear sprockets of the bicycle. The driven rings of the intermediate shaft are smaller than the respective crossover chainrings so that the intermediate shaft is driven at a higher speed than the respective pedal cadences. So that a given gear ratio variation between largest and smallest drive rings may be achieved with a smaller arithmetic gap between the number of teeth on the drive rings. Ground clearance may be greater that of a conventional tandem bicycle due to use of smaller driven and driving chainrings and elevated positioning of the intermediate shaft. The independent freewheeling of the cranksets allow each rider to independently control the rotational position of his or her crankarms for purposes such as clearing obstacles. The present invention also allows the riders to selectively change the relative rotational orientations of the cranksets to allow, for example, pedalling in full synchronization or 90.degree. out of phase to achieve a smoother application of pedalling force.