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 &# 39 ; s knees and a dynamically adjustable tilt - in - space configuration with the tilt axis being near the user &# 39 ; 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 .