For the 1986 season, Murray designed the radical low-line BT55 chassis, whose aim was to significantly reduce the car's drag and lower its centre of gravity. BMW produced the M12/13/1 engine, which was tilted sideways to fit in the reduced space allocated to the engine. Despite its theoretical advantages, the BT55 proved uncompetitive, suffering from poor traction and numerous mechanical failures caused by oil scavenge problems in the tilted engine. Moreover, the team suffered the death of Elio de Angelis in a testing accident after four races; his replacement Derek Warwick and team returnee Patrese scored two points between them all season. The Arrows team also slipped backwards, scoring just one point with Boutsen, Surer and Christian Danner, and also lost Surer's services mid-season when the Swiss driver was seriously injured in a rallying accident. BMW's most successful 1986 partnership was thus with the new Benetton team, which scored 19 points, won the Mexican Grand Prix and took two pole positions with Berger and Teo Fabi. Arrows and Benetton continued to use the original "upright" version of the M12/13 engine.