The design of the successful BT series cars, equipped with the BMW 4L turbo from previous seasons, had reached the limits of development. Therefore, for the 1986 season, designers Gordon Murray and David North created the new BT55, an entirely new car, very long, wide, and low, that forced the driver into an almost reclined position. As usual, Murray designed a single-seater with very clean lines and, with its “flat” shape, sought to deliver the cleanest possible airflow to the new, large rear wing by minimizing the height of the engine cover. This required BMW engineers to redesign the engine, tilting it 72° to one side.
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| BRABHAM BT55, Elio de Angelis Imola, San Marino GP 1986 |
However, the South African technician’s choices proved disastrous for the Bavarian engine, nullifying the strengths of the original design. The engine block was reshaped to allow the 72° tilt required by Murray, but the cylinder head and cylinders remained unmodified. Moreover, the innovative electronic ignition and turbo pressure management system clashed with the outdated Bosch-Kugelfischer mechanical injection, which was far less efficient than the modern Bosch-Motronic used by TAG-Porsche or Hitachi by Honda. Reducing the fuel tank capacity to 195 liters forced BMW engineers to run the engine on a leaner mixture, resulting in even poorer performance. Additionally, since the lubrication system wasn’t adapted to the engine's new inclination, the BT55 suffered oil return issues in right-hand corners due to centrifugal force. Another issue arose from the gearbox placement. The tilted engine required the gearbox to be mounted to the side, prompting Weismann to develop a new 7-speed transverse gearbox with three output shafts, which proved fragile and hard to fine-tune.
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| BRABHAM BT55, Elio de Angelis Montecarlo, Monaco GP 1986 |
The new chassis, Brabham's first entirely made of carbon fiber, unlike previous models which combined aluminum and carbon, provided better stiffness. However, the BMW engine wasn’t rigid enough to serve as a stressed member, forcing engineers to add a heavy auxiliary subframe, pushing the BT55’s weight up to 555 kg. From the initial tests, the car showed major engine efficiency problems, along with handling and weight distribution issues. The radiator placement, too far forward, compromised traction, already suffering due to the extremely long wheelbase of 3048 mm, caused by the car’s narrow and low chassis design. These problems weren’t resolved before the championship began, with drivers Riccardo Patrese and Elio de Angelis struggling mid-pack before being forced to retire.
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| BRABHAM BT55, Derek Warwick Paul Ricard, French GP 1986 |
The BT55 project proved to be a failure, and despite minor adjustments to the exhaust system and weight distribution, little changed. On May 14th, during a private testing session at the Paul Ricard circuit in Le Castellet, Elio de Angelis' BT55 went off track at high speed after the rear wing failed. The car crashed into the barriers and immediately caught fire. Due to the private nature of the test, emergency services were scarce and slow to arrive. The Roman driver died 19 hours later from inhalation of toxic fumes released by the burning vehicle. The accident cast an even darker shadow over Murray’s flawed design. The team even considered reverting to the 1985 BT54 and the older “upright” engines, but ultimately chose to continue the season with the BT55. To replace the ill-fated de Angelis, experienced British driver Derek Warwick was brought in and contributed by suggesting further updates.
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| BRABHAM BT55, Riccardo Patrese Montecarlo, Monaco GP 1986 |
With team owner Bernie Ecclestone increasingly focused on managing the Formula 1 business rather than his team, and amid a chaotic and ineffective team environment, Gordon Murray decided at the end of the season to move to McLaren to work on a road-going GT car program. He left the team that had made him one of the most brilliant engineers of the ’70s and ’80s. Three years later, when he was called to work with McLaren’s racing division, he revisited several fundamental BT55 concepts, applying them to the MP4/4, one of the most successful cars in history. Additionally, BMW decided midway through the 1986 season to withdraw from Formula 1 at the end of the championship. However, Brabham insisted that the Bavarian manufacturer continue to supply engines in 1987 under the existing contract, albeit without official BMW support and under the care of Swiss engineer Heini Mader.
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