A disc recliner operatively coupling a seat back to a seat cushion to allow selective pivotal movement of the seat back relative to the seat cushion about a pivot axis extending in an axial direction, the disc recliner comprising: a first plate adapted to be fixedly secured to the seat cushion , the first plate including a first plurality of teeth disposed therearound; a second plate adapted to be fixedly secured to the seat back and rotatably coupled to the first plate , the second plate including a second plurality of teeth disposed therearound, wherein a tooth count of the first plurality of teeth does not equal a tooth count of the second plurality of teeth ; a flex spline including a flexible wall having a third plurality of teeth disposed therearound, wherein a tooth count of the third plurality of teeth equals the tooth count of the first plurality of teeth ; Characterised by a wave generator (28; 80) having an outer profile causing a portion of the third plurality of teeth to meshingly engage with the first plurality of teeth and the second plurality of teeth ; wherein the wave generator (28; 80) includes a cam (55; 82) having a plurality of spaced apart lobes (56; 84) extending outwardly in a radial direction defining the outer profile and a plurality of rollers (60; 86) extending around the perimeter of the cam (55; 82) for direct contact between the lobes (56; 84) and the flexible wall of the flex spline for forcing the third plurality of teeth of the flex spline to meshingly engage with the first and second plurality of teeth , wherein the second plate rotates relative to the first plate , thereby causing pivotal movement of the seat back relative to the seat cushion in response to rotation of the wave generator (28; 80). a first plate adapted to be fixedly secured to the seat cushion , the first plate including a first plurality of teeth disposed therearound; a second plate adapted to be fixedly secured to the seat back and rotatably coupled to the first plate , the second plate including a second plurality of teeth disposed therearound, wherein a tooth count of the first plurality of teeth does not equal a tooth count of the second plurality of teeth ; a flex spline including a flexible wall having a third plurality of teeth disposed therearound, wherein a tooth count of the third plurality of teeth equals the tooth count of the first plurality of teeth ; Characterised by a wave generator (28; 80) having an outer profile causing a portion of the third plurality of teeth to meshingly engage with the first plurality of teeth and the second plurality of teeth ; wherein the wave generator (28; 80) includes a cam (55; 82) having a plurality of spaced apart lobes (56; 84) extending outwardly in a radial direction defining the outer profile and a plurality of rollers (60; 86) extending around the perimeter of the cam (55; 82) for direct contact between the lobes (56; 84) and the flexible wall of the flex spline for forcing the third plurality of teeth of the flex spline to meshingly engage with the first and second plurality of teeth , wherein the second plate rotates relative to the first plate , thereby causing pivotal movement of the seat back relative to the seat cushion in response to rotation of the wave generator (28; 80). <EOS>