Abstract: Upper and lower relatively rotatable members are provided with the upper member angularly displaceable relative to the lower member about an upstanding axis. The upper member includes first front and rear portions disposed forward and rearward of the axis and a seat amount is supported and projects upwardly from the upper member. A seat support member including second front and rear portions overlying the first front and rear portions is provided and is pivotally attached to the mount for oscillation about a horizontal transverse axis adjacent the upstanding axis. The seat support member may support a seat therefrom with the front and rear portions of the seat overlying the second front and rear upper member portions and expansion springs are connected and extend between the first and second front portions yieldingly resisting upward movement of the second front portion relative to the first front portion.