1955 Buenos Aires Grand Prix

The 11th Gran Premio Ciudad de Buenos Aires was a Formula Libre motor race held on 30 January 1955 at the Autódromo 17 de Octubre in Buenos Aires. It pitted regular 2500cc F1 cars against Mercedes F1 chassis that were fitted with larger sportscars engines of the upcoming Mercedes-Benz 300 SLR.

It followed the 16 January 1955 Argentine Grand Prix F1 race that opened the 1955 World Championship of Drivers season. Held at the same circuit in hot weather, the GP was won after 96 laps by Fangio while suffering burns to his legs in his Mercedes-Benz W196. In between, on a street circuit, the 23 January 1955 1000 km Buenos Aires sports cars race was held, opening the FIA 1955 World Sportscar Championship season with a private Ferrari winning points for the brand.

The new Mercedes-Benz 300 SLR sports car chassis was not ready yet, despite being closely related to the Mercedes-Benz W196 F1 cars. Some of the enlarged 3.0 litre pump gas sportscar engines were ready, and they were tested in the four F1 chassis, replacing the high revving high compression high octane fuel 2.5 litre F1 engines.

The Libre race was held over two heats of 30 laps, with the winner decided by aggregate time. The event was won by Juan Manuel Fangio in a Mercedes-Benz W196, his teammate Stirling Moss was second, Kling 4th, Herrmann DNF.

José Froilán González shared two Ferrari 625, for third place with Maurice Trintignant, and for 10th with Farina.