Bentley 6½ Litre & Speed 6 Tyres

Between 1926 and 1930, the Bentley 6½ Litre and the high-performance Bentley Speed Six were rolling chassis. The Speed Six, which debuted in 1928, would go on to become Bentley's most successful racing model. By 1924, Mr Bentley had chosen to construct an automobile with a bigger chassis than the 3 Litre and a smoother, more powerful engine than the 3 Litre. The new chassis would be more suited to the large and heavy limousine bodywork that some people had been putting to his sports car chassis. The resulting vehicle would be more elegant and well-suited to pleasant general driving. Bentley's straight-6 engine, like the four-cylinder engine, had an overhead camshaft, four valves per cylinder, and a single-piece engine block and cylinder head cast in iron, which removed the need for a head gasket. The Bentley 6½  Litre produced 147 horsepower at 3500 RPM in standard configuration.

Despite being based on the 3 Litre engine, the 6½ engine has several advancements. The cone-type clutch of the 3 Litre was replaced by a dry-plate design with a clutch brake for quick gear changes. The vehicle had power-assisted four-wheel disc brakes with finned drums. The driver could adjust all four brakes to correct for wear while the car was driving by using a proprietary compensating system, which was especially useful during races.

The Bentley Speed Six chassis debuted in 1928 as a more sporty version of the Bentley 6½ Litre. The Speed Six's engine generated 180 horsepower thanks to a single-port block, two SU carburetors, a high-performance camshaft, and a compression ratio of 5.3:1 at 3500 rpm. Customers may choose the Speed Six chassis in three different wheelbase lengths: 138 inches, 140.5 inches, and 152.5 inches. The racing version of the Speed Six featured a 132-inch wheelbase and a 6.1:1 compression ratio engine that developed 200 horsepower (at 3500 rpm), enough for the 6 Speed to win the 24 Hours of Le Mans in both 1929 and 1930!