The March 721 was a Formula 1 racing car raced in the 1972 season of Formula One and built by March Engineering.
It was the successor of the March 711 and was up against strong cars in the season. It was a change as in 1971 March had jumped to be one of the top Formula 1 constructors. The 721 was designed and built for customers like Frank Williams and Guenther Hennerici.
The 721X was destined for the factory team. The X had the monocoque of the 721, the rear springs were however highly articulated. Designer Frank Costin wanted to create a lower moment of inertia by focusing most of the weight of the car in the middle of the vehicle. In theory, this design was understandable. The front tires were constantly overloaded, so was over-and understeer.
The 721G was built to avert an utter failure in the 1972 season. The 721G had a conventional Formula 2 chassis which was then adjusted for Formula 1. Suspension and brakes were from the 721, as was the Cosworth V8 engine. Ronnie Peterson reached third in the G-type at the German Grand Prix.