A seat supporting assembly (24) for supporting a seat (18), the assembly comprising a base (25) including a substantially elongated guiding rod (58), a seat support (36), a seat support-to-base linking member (56) pivotally coupled to the seat support (36) and sliding on the base guiding rod (58), a substantially elongated tilting member (60) having a guiding groove (66) and being pivotally attached to the seat support (36) and to the base (25). An actuating assembly (44) is coupled to the base (25) and includes a motion transmitting member (68) mounted within the guiding groove (60). The force from the actuating assembly moves the tilting member (60) according to the geometry of the guiding groove (66), which causes the seat supporting assembly (24) to move between tilted and upright configurations by pivoting the tilting member (60) relative to the seat support (36) and the base (25) and substantially simultaneously moving the seat support-to-base linking member (56) longitudinally relative to the guiding rod (58). The assembly is designed to maintain the location of the center of gravity of a user as the seat tilts rearwardly by automatically moving the seat forwardly during tilting. The guiding groove (66) in the tilting member (60) may be curved such that the tilting motion occurs with a constant angular velocity The seat assembly is particularly useful for wheelchairs.La présente invention concerne un ensemble soutenant un siège (24) destiné à soutenir un siège (18), lensemble comprenant une base (25) comprenant une tige de guidage sensiblement allongée (58), un support de siège (36), un élément de liaison support/base du siège (56) couplé avec faculté de rotation au support de siège (36) et coulissant sur la tige de guidage de la base (58), un élément dinclinaison sensiblement allongé (60) comportant une rainure de guidage (66) et étant fixé avec faculté de rotation au support de siège (36) et à la base (25). Un ensemble dactionnement (44) est couplé à la bas
