Abstract: A wheelchair system comprises a substantially rigid seat adapted to be mounted on at least two alternative types of carriages having different drive arrangements each comprising a pair of molded plastic side frames which are interconnected by a bracing mechanism to permit the side frames to be folded together for collapsing the chair or spread apart for erecting the chair. A connecting system including locators which allow the seat to be placed on an approximately fully spread carriage and then to locate the side frames at the correct spacing from one another in order to ensure complete spreading of the carriage, and additionally retainers which allow the seat to be moved into a position in which it cannot be lifted from the thus spread carriage, the retainers allow positive engagement of the seat with the chair with the ability to spread the carriage solely by downward pressure on the seat, thereby enabling a disabled user of the wheelchair to be able to place the seat on the carriage ready for use.