In the late 1960s, Jim Hall of Chaparral, first introduced "ground effect" downforce to auto racing. In the mid-1970s, Lotus engineers found out that the entire car could be made to act like a giant wing by the creation of an airfoil surface on its underside which would cause air moving relative to the car to push it to the road. Applying another idea of Jim Hall's from his Chaparral 2J sports racer, Gordon Murray designed the Brabham BT46B, which used a separately-powered fan system to extract air from the skirted area under the car, creating enormous downforce. After technical challenges from other teams, it was withdrawn after a single race. Rule changes then followed to limit the benefits of 'ground effects' – firstly a ban on the skirts used to contain the low-pressure area, later a requirement for a 'stepped floor'.