In 1979, a significant amount of progress was made in aerodynamics and to challenge Lotus, Forghieri realised he had to follow their lead and design a ground effect car for 1979. The 312T4, introduced at the 1979 South African Grand Prix was closely based on the 312T3. Its origins placed restrictions on the aerodynamic design since the T series had never been designed with ground effect in mind. The 312T4 monocoque was designed to be as narrow as possible, to take advantage of ground effects, but this was limited by the width of the flat 12 engine.