The Sauber C9 (later named the Sauber Mercedes C9 or Mercedes-Benz C9) was a Group C prototype race car introduced in 1987 as a continuation of the partnership between Sauber as a constructor and Mercedes-Benz as an engine builder for the World Sportscar Championship. The C9 replaced the previous Sauber C8. For its debut season in 1987, the cars were run by Kouros Racing, named after the fragrance brand of its sponsor, Yves Saint Laurent, although officially backed by Mercedes-Benz. The team managed a mere twelfth in the teams standings, scoring points in only a single round. For 1988, Kouros was dropped as a sponsor, forcing the team to be renamed Sauber Mercedes. As a result, Mercedes used AEG-Olympia for sponsor – AEG being owned by Daimler-Benz at the time. They managed to finish second in the championship behind Silk Cut Jaguar with five wins for the season. Unfortunately at the 24 Hours of Le Mans, the team suffered an embarrassing setback when they were forced to withdraw due to concern over their Michelin tires.
Finally, in 1989, the car was able to achieve great success. Beside replacing the black color scheme for its national plain silver scheme, reducing AEG as a minor sponsor, the older M117 5.0L turbocharged V8 engine was upgraded to the M119, which replaced steel heads with new aluminium. The C9 was able to win all but one race in the 1989 season, including the 24 Hours of Le Mans. During qualifying for Le Mans, the C9 recorded a speed of 247 mph (398 km/h) on the Mulsanne Straight, a record. Mercedes driver Jean-Louis Schlesser would end up taking the driver's championship that season.
The C9 would be replaced by the Mercedes-Benz C11 from the second race onwards of the 1990 season, where it took one final win.
Reaching 248.0 mph (400 km/h) during the qualifying sessions of the 1989 24 Hours of Le Mans, the Sauber C9 has set one of the fastest top speeds ever in the history of the competition at Le Mans. These speeds led to the cessation on the huge Le Mans Mulsanne Straight and the introduction of two chicanes, from 1990 onwards.
The C9's top speed was only beaten by the WM Peugeot prototype, with a speed of 251.1 mph (405 km/h) in the 1988 race. However the WM, optimized for a low drag setup and high straight line speed, suffered from handling problems elsewhere on the circuit and the engine was prone to overheating. Indeed the car's fastest time was set with tape applied over the ducting for aerodynamic purposes and was withdrawn as soon as a new record was set to avoid an expensive rebuild.