Aerodynamic downforce slowly gained importance in car design with the appearance of aerofoils during the late 1960s. During the late 1970s, Lotus introduced ground-effect aerodynamics (previously used on Jim Hall's Chaparral 2J during 1970) that provided enormous downforce and greatly increased cornering speeds. So great were the aerodynamic forces pressing the cars to the track (up to five times the car's weight), extremely stiff springs were needed to maintain a constant ride height, leaving the suspension virtually solid, depending entirely on the tyres for any small amount of cushioning of the car and driver from irregularities of the road surface.