The seat on a kart should be tight, so that you can sense every motion of the kart with your body. Also, it will prevent you from bouncing around uncontrollably in the curves, since a kart does not have any seat belts. Pedded seats are nice, but not a necessity. By moving the seat around or up and down, you can significantly change the handling of the kart, since you will have achieved a different weight distribution. The seat is mounted to the kart via seat struts.