1930s Alfa Romeo P3 Tipo with Dubonnet front suspension
Dubonnet suspension was a system of independent front suspension and steering popular mainly in the 1930s and 1940s. Not very durable unless exactingly maintained, it was soon replaced by other versions. It consisted of a rigidly mounted axle beam in which the sprung steering and suspension arms pivoted aound kingpins mounted of the ends of the axle. The wheels themselves were mounted onto stub axles, suspended from the kingpins. The system featured an encased coil spring and shock absorber, which sealed in the oil needed to lubricate and protect the suspension parts. This was also the weakness of the layout, as any leaks would have negative effects on ride and durability.
The system was invented by French engineer and designer André Dubonnet (heir to the Dubonnet vermouth fortune), and built into his Hispano-Suiza based special of 1933.He sold it to General Motors who adapted it as their "Knee-action ride", but the system was also used by many others including Fiat, Alfa Romeo, and Simca.