After almost a day of testing at Riverside International Raceway in the brutally hot Southern California desert summer weather, Miles approached the end of the track's 1-mile (1. 6 km), downhill back straight at top speed (200-plus mph) when the car suddenly looped, flipped, crashed and caught fire. The car broke into pieces and ejected Miles, killing him instantly. The car had suffered precisely the sort of crash damage the honeycomb construction was designed to prevent. As a result, the aerodynamics of the J-car were greatly modified to correct the rear-end lift generated at race speeds. Ford officials, under pressure after the second of two fatal accidents in the programme in five months, also ordered a NASCAR-style steel tube rollover cage to be installed in future versions of the car.  The death of 47-year-old Miles, following that of 46-year-old Hansgen, led Ford to favour younger drivers in subsequent race entries.  The significantly revised J-car, renamed the Ford Mk IV, won the only two races in which it was entered: the 1967 Sebring (Fla. ) 12 Hours, and the 1967 24 Hours of Le Mans. The steel roll cage in the Mk IV (mandated as a direct result of Miles's death) probably saved the life of Mario Andretti, who crashed violently during the 1967 24 Hours of Le Mans but escaped.