Brabham Bt55

By 1985, Brabham had reached the aerodynamic development limit of its BT52–BT53–BT54 series. The 1985 car, powered by the tall BMW M12 straight-four, won only one race — Nelson Piquet's victory in France — prompting Murray to pursue a radical rethink. With ground effect banned, the rear wing again generated much of the car's downforce, but its effectiveness was blunted when bodywork upstream disrupted airflow. The same challenge had led 1950s designers to tilt engines slightly; Murray took the idea far further. Both Brabham and gearbox supplier Weismann later claimed credit for the core idea of tilting the tall BMW engine so dramatically that the car could run extremely low bodywork and feed the rear wing with clean, undisturbed air. The driver was reclined at roughly 30 degrees, a posture common in the 1960s but rare by the 1980s.

The BT55 was Brabham's first fully composite monocoque, built from carbon fibre and Kevlar over a Nomex honeycomb, reinforced by machined aluminium bulkheads. Murray had earlier persuaded Ecclestone to finance a full crash test of a BT49 to understand composite behaviour in impacts before committing to the design. At Murray's request, BMW produced a special variant of the M12 with the engine block tilted 18 degrees from horizontal — almost on its side. The changes from the standard unit were mainly confined to the oil scavenging system and its mounting cradle; the engine remained a non-stressed component. The offset power takeoff created by the side-mounted position required a bespoke American-made Weismann 7-speed, 3-shaft gearbox.

Nelson Piquet departed Brabham after seven seasons and two world championships, joining Williams. Marc Surer also left, replaced by Elio de Angelis alongside returning driver Riccardo Patrese. The aerodynamic concept delivered as intended on fast circuits: the cars ran less wing than rivals yet remained among the quickest in a straight line, with Derek Warwick recording the BT55's ultimate top speed of 347 km/h at Monza, and 344 km/h at the Österreichring. However, the tilted engine and bespoke gearbox produced persistent reliability failures including oil surge and sluggish throttle response, compounding the turbo lag inherent to the single-turbo four-cylinder BMW unit. On slower circuits — Monaco, Detroit, Jerez, the Hungaroring — where acceleration out of corners mattered more than top speed, the Brabham was uncompetitive. Patrese qualified sixth at Monaco while de Angelis qualified last, 20th; at Imola, both drivers were nearly four seconds off pole. Brabham scored just two championship points across the entire season, both sixth-place finishes recorded by Patrese at San Marino and Detroit.

De Angelis was killed during a private test session at the Circuit Paul Ricard in France. The car survived the accident relatively intact and de Angelis initially appeared to have only minor injuries, but a shortage of track marshals meant he remained trapped and suffered oxygen deprivation from fire before help arrived. He died from smoke inhalation 29 hours after the crash at a hospital in Marseille. The accident prompted a thorough review of testing safety practices, resulting in requirements for additional marshals, medical staff, and a mandatory medical evacuation helicopter at test sessions. Brabham entered only one car for Patrese at the Belgian Grand Prix immediately following the tragedy. From the Canadian Grand Prix onwards, British driver Derek Warwick — who had been racing for TWR Jaguar in sportscar racing after missing a Lotus seat — joined the team. Ecclestone noted that Warwick was reportedly the only available top-level driver who did not contact him seeking the vacant seat in the days after de Angelis's death.

At the end of 1986, Murray left Brabham for McLaren, where he replaced John Barnard as Technical Director. He later assessed that the BT55's failure stemmed from attempting too steep an engine tilt within the available time, combined with the BMW's structural incompatibility with the horizontal position — one-way oil drainage worked in one direction only, producing incurable oil surge in corners, while the weight distribution created dynamic centre-of-gravity shifts that hurt traction. Murray maintained that the lowline concept itself was sound and would have worked with a more compact V6 engine. The 1988 McLaren MP4/4, which Murray designed and which proved dominant, is frequently linked to the BT55 concept, though that connection has been disputed, with some attributing the MP4/4 primarily to the preceding Steve Nichols-designed MP4/3. Brabham regrouped with the more conventional BT56 for 1987 but was forced to retain the tilted BMW engine, as the manufacturer had sold rights to the conventional upright version to Megatron for use by Arrows and later Ligier. BMW exited Formula One entirely at the end of 1987. Ecclestone then sold Brabham to Alfa Romeo, and the team missed the 1988 season.