They were light-alloy drums on all four wheels[5] with power-assist[2][3] the first in the industry,[citation needed] driven with a special shaft from the transmission.

When the car was decelerating, its own momentum drove the brake servo to provide additional power.

[2][6] Woolf Barnato piloted a Boulogne to eight international records, including a 92 mph (148 km/h) average over 300 mi (480 km), at Brooklands in 1924.

[7] Powered by a 7,982 cc (487.1 cu in) straight 6 (estimated to produce 195 hp (145 kW)),[8] Dubonnet demanded a maximum body weight of 100 lb (45 kg),[5] and the aircraft maker Nieuport- Astra complied with tulipwood strips[7] (later determined to have been mahogany),[citation needed] fastened to an aluminium frame with thousands of tiny rivets.

[2] A six-wheeled H6A was ordered by the King of Greece, but after his abdication was purchased by the motion picture director D. W. Griffith.

To cope with the poor fuels available, the compression ratio had been limited to 4.5:1 and engine power to 100 hp (75 kW) at 1800rpm.