sentences:  The car proved to be very fast but Gilles Villeneuve found the handling to be very difficult, calling the car "a big red Cadillac".According to Villeneuve's teammate Didier Pironi and English engineer Harvey Postlethwaite, who arrived at Ferrari well into the 1981 season, it was not the chassis that was the main cause of the car's handling problems, but the very bad aerodynamics of the car.Postlethwaite later said that the 126CK "had a quarter of the downforce that the Williams or Brabham had that year".