Abstract: A seat tilting mechanism comprising a main body, a seat support, a backrest support and an articulation mechanism comprising a lever, a first portion of which defines along with a first arm, the seat support and the main body a first quadrilateral hinge, and a second portion of which defines alone with a second arm, the backrest support and the main body a second quadrilateral hinge. Interior corner angles and lengths of each side of the first and second quadrilateral hinges are such that a predetermined angular displacement ratio of the backrest support in relation to the seat support is provided. An extension resistance device is mounted between the main body and the first portion to provide resistance to rotation of the lever. A first end of the extension resistance device is rotationally mounted to the lever at a first mounting point, which is located between the midpoint and upper point, and is angularly displaced from a line extending between the midpoint and the upper point.

Abstract: A seat tilting mechanism comprising a main body, a support member rotationally mounted to said main body, and a first extension coil spring mounted between said main body and said support member to provide resistance to rotation of said support member, in which said seat tilting mechanism further comprises a second extension coil spring and an engagement mechanism which engages said second extension coil spring for resistance to rotation of said support member when said first extension coil spring reaches a pre-determined point of extension.