The 300 SLR was not derived from the 1952 W194 Le Mans racer or the 1954 300SL Gullwing, but was instead based on the successful 1954–1955 Mercedes-Benz W196 Formula One car, with the engine enlarged to 3.0 litres for sports car racing. All design work was carried out by Daimler-Benz’s chief designer, Rudolf Uhlenhaut. The car’s engine, designated M 196 S, was a 3-litre straight-eight, producing 302 PS (222 kW).
The 1955 racing season began with Juan Manuel Fangio winning the Argentine Grand Prix for Mercedes, though he suffered burns to his leg in the process. Fangio also won the Buenos Aires Grand Prix in a Mercedes-Benz W196 Formula 1 car fitted with the enlarged 3-litre engine from the 300 SLR. The 1000 km Buenos Aires race saw a 1-2 victory for Ferrari, after the works entries were disqualified, with the third-place Maserati earning four points for the brand.
Following intense preparation, Stirling Moss won the 1955 Mille Miglia in a 300 SLR, setting a record average speed of 157.650 km/h (97.96 mph) over 1,600 km (990 mi). He was assisted by co-driver Denis Jenkinson, a motor-racing journalist who provided pacenotes based on prior reconnaissance. Juan Manuel Fangio finished second in a sister car.
The 1955 24 Hours of Le Mans was overshadowed by a horrific accident involving Pierre Levegh in a 300 SLR. While attempting to avoid an Austin-Healey that had swerved to avoid a Jaguar making a pit stop, Levegh’s car launched into the air and crashed, igniting due to the magnesium alloy bodywork. Eighty-three spectators and Levegh lost their lives, marking the highest-fatality accident in motorsport history. The remaining 300 SLRs were withdrawn from the race.
Despite several races being cancelled, Mercedes continued to compete in non-championship sportscar races, achieving wins at the Eifelrennen in Germany and the Swedish Grand Prix. The 300 SLRs then secured a 1–2 finish at the 1955 Targa Florio in Sicily, earning Mercedes the World Sportscar Championship title with a two-point lead over Ferrari.
Two of the nine 300 SLR chassis were built as closed coupés, nicknamed the “Uhlenhaut Coupé”. These road-legal racers featured gull-wing doors and resembled the 300 SL production car. Rudolf Uhlenhaut appropriated one of these coupés as his personal vehicle, capable of reaching speeds approaching 290 km/h (180 mph).
Inspired by the 300 SLR Uhlenhaut Coupé, the Mercedes-Benz SLR McLaren grand tourer was jointly developed by Mercedes-Benz and McLaren Automotive, debuting in 2003. It featured a hand-built 5.4-litre, supercharged V8 engine and was available in coupé and roadster versions, as well as other specialised variants, with production ending in early 2010.
The 300 SLR featured a front mid-engine layout, with the engine positioned behind the front axle for improved weight distribution. Its chassis was constructed from a brazed steel tube spaceframe and clad in ultra-light Elektron magnesium-alloy bodywork, resulting in a low vehicle mass of 901 kg (1,986 lb) for the roadster and 1,117 kg (2,463 lb) for the coupé. The engine, canted to the right at 53 degrees, produced 310 PS (228 kW) at 7400 rpm and featured direct fuel injection. To enhance braking, the car used large diameter, inboard-mounted drum brakes.