more than 80 lives after Pierre Levegh's Mercedes left the track and ploughed into spectators. Thereafter, he concentrated on his engineering. By the end of 1956, although still a member of the Jaguar works team, Rolt retired from active racing to devote his full efforts to the Ferguson development programme. Engineering career After the war, Rolt returned to form part of Rolt Dixon Research, with his mechanic, Freddie Dixon, to work on an idea that they had considered before the war: four-wheel drive. The company they formed also pioneered the viscous coupling. This eventually led to backing from tractor magnate Harry Ferguson and gave rise to the development of the Ferguson P99 four-wheel drive F1 car. Rolt subsequently built Indianapolis 500 track-racing 4WD cars for the American STP Corporation, and Ferguson transmissions appeared in the Lotus 56, Novi-Ferguson and STP-Paxton Turbocar Indy Cars of 1964 to 1969. With the technical director Claude Hill and the project engineer Derek Gardner, Rolt was among the unsung backroom heroes of British racing development. When Ferguson Development closed, Rolt founded FF Developments in 1971, converting cars, vans and ambulances to four-wheel drive. During the 1980s, major automotive manufacturers finally saw advantages in all-wheel drive technology, and the company became a major technology partner of Ford, Chrysler, Audi, Fiat and General Motors. In 1994, the business was sold to Ricardo, who continued the development of "smart" transmissions using Rolt FFD and Ferguson experience. Rolt was immensely proud that the Audi sports cars that have dominated the 24 Heures du Mans and the American Le Mans Series endurance championships since 2000 used Ricardo transmissions. The F1 Tractor By the early 1960s Rolt and FF Developments had decided that it would build a 4WD racing car to demonstrate the value of four-wheel drive technology. Rolt helped to design, and also tested the Ferguson P99. Although Rolt was more than capable of driving the car fast enough for test purposes, Jack Fairman was called in to race it in the 1961 British Empire Trophy and 1961 RAC British Grand Prix at Aintree, proving without doubt the four-wheel drive allied to the Dunlop Maxaret braking system was substantially superior in the wet. The P99 was run under the banner of Rob Walker Racing and became the only 4WD car to win a Formula One race, when in the hands of Stirling Moss it won the 1961 Oulton Park Gold