Abstract: A single rider bicycle is adapted to be transformable to a two rider bicycle, and comprises a stationary tubular framework structure and an extendible tubular framework structure. The structures are telescopically coupled. The stationary structure includes a stationary saddle and support means for a removable saddle. A permanent pedal crank is disposed upon said stationary structure while the extendible structure includes a pedal crank. Removable coupling means are provided for coupling the permanent and removable pedal cranks when the bicycle is extended to its tandem position. Means are further provided for enabling horizontal and vertical adjustment of the removable saddle.