A modular wheelchair assembly is adapted to be reconfigured between a fixed angle of tilt, a dynamically adjustable tilt-in-space configuration with the tilt axis being near the user's knees and a dynamically adjustable tilt-in-space configuration with the tilt axis being near the user's center of gravity. The reconfiguration is achieved by modifying a limited number of selectively removable components of the support assembly or the pivot assembly of the wheelchair.