Ground effect had been banned at the end of 1982, and so the car was built around a flat-bottomed arrangement. It featured enlarged wings to try to claw back as much of the lost downforce as possible. It was also the first Formula One car to feature exhaust routing such that it increased the downforce created by the diffuser. René Arnoux had left the team to be replaced by Eddie Cheever, whilst Alain Prost was now undisputed no.1 driver. The RE40 was designed around his driving style, and he racked up many miles of testing to avoid the unreliability of the previous two seasons.