In practice for Le Mans in 1952, Mercedes experimented with an air brake that rose up at the rear of the coupe top. The air brake not used for the race but the idea re-appeared on the 300SLR for Le Mans in 1955 with a full-width flap behind the open cockpit.
The scrutineers asked for the window area to be doubled to the regulations for the rear window of a saloon car at 84 square inches.
