The Mercedes-Benz 300 SLR (W196S) was a sportscar racing car that won the 1955 World Sportscar Championship season.

Technical highlights

Despite the misleading name, the Mercedes-Benz 300 SLR was based neither on the famous 1954 300SL (W198) Gullwing road car, nor the earlier 1952 (W194) race car, although it bears a strong resemblance to both (including, in the coupe version, the distinctive 'gullwing doors'). Instead, it was based on the 1954–1955 Formula 1 Mercedes-Benz W196 race car; it was Mercedes' marketing department, considering 'W196S' an uninspiring name, who ordered the name '300 SLR'. It is generally accepted that this name references the car's lightweight construction as 'Sport Leicht Rennen'.

The car was designed by longtime Mercedes designer Rudolf Uhlenhaut. It was a front-mid-engined design (where the engine block is squarely behind the front axles) to give more neutral front/rear weight distribution. It used a spaceframe chassis and magnesium-alloy (Elektron) bodywork, which has a specific gravity of just 1.8 (for reference, the S.G. of iron is 7.8), both of which contributed to a dry weight of just 880 kg (1,940 lb). The preceding Formula 1 car's 8-cylinder in-line engine was used, increased in capacity from 2,496.87 cc (76.0 x 68.8 mm) to 2,981.70 cc (78.0 x 78.0 mm). This boosted output from 290 bhp (220 kW) at 8,500 rpm to about 310 horsepower (230 kW) at 7,400 rpm, depending on the intake manifold; maximum torque of 318 N·m (235 lb·ft) at 5,950 rpm (193.9 psi (1,337 kPa) BMEP). The engine was longitudinally mounted and canted at a 33-degree angle to lower its profile for aerodynamic reasons, resulting in the distinctive bonnet bulge on the passenger side of the car. The engine was also unusual in having desmodromic valve actuation instead of springs. Its war time derived fuel injection was still a novelty then. The engine protruded some way back into cockpit, forcing drivers of the monoposto to straddle the driveshaft and clutch bellhousing with his feet to reach the pedals. To reduce crank flexing, power takeoff from the engine was at the center of the engine, via a gear, rather than at the end of the crankshaft. This was not the only oddity of the drivetrain - the car was fitted with vast inboard drum brakes which dwarfed the car's 16"-wheels; the unusual shaft-linked brakes were originally to have been part of a planned four-wheel-drive system which never came to fruition. The rear independent suspension used a low roll centre swing axle system, where a beam attached to each hub was mounted on the opposite side of the chassis. Thus, the beams were aligned slightly differently and crossed over in the centre line. Cornering forces did not jack the car up, as occurs with short swing axles.

The car's fuel itself was also unusual - a high-octane fuel mixture of 65 percent low-lead gasoline and 35 percent benzene; in some races, alcohol was also used to further increase performance. As a rule, the car left the starting line with 44 gallons of fuel and more than nine gallons of oil on board, although Moss and Jenkinson began their assault on the 1955 Mille Miglia with as much as 70 gallons of fuel in the tank.

At Le Mans in 1955, the 300 SLRs were also equipped with "air brakes" similar in principle to those used on aircraft - this was a large hood that hinged up behind the occupants in order to slow down the cars at the end of the fast straights. The idea for this "wind brake" came from director of motorsports Alfred Neubauer, who was looking to develop a system to reduce the wear on the huge drum brakes and tires during long-distance races such as Le Mans and Reims. Neubauer foresaw that wind resistance would slow the car especially at Le Mans, as the French track's layout forced drivers to use the brakes hard and often to bring the car down from its maximum speed - around 180 mph (290 km/h) - to as little as 25 mph. In tests the 0.7m² (7.5 ft²) light-alloy spoiler slowed the car dramatically and improved cornering. In addition, this innovation was required as the car's traditional drum brakes were inferior to the new disc brakes of main rival Jaguar.

The SLR also had two seats, as required for sports racing cars of the day. In some racing events a co-driver, mechanic or navigator was given a ride. In the 300 SLR's short career, this was only during the Mille Miglia, as the 1955 Carrera Panamericana was cancelled due to the Le Mans accident. On short circuits (this includes the Targa Florio) passengers were not helpful, thus the passenger seat was covered and the passenger windshield removed to improve aerodynamics.

Nine W196S chassis were built.

Triumph and tragedy

Stirling Moss won the 1955 Mille Miglia in a 300 SLR with an average speed of 157.65 km/h (97.96 mph) over 1,600 km (990 mi). He was assisted by his co-driver Denis Jenkinson, a British motor-racing journalist, who informed him with previously taken notes, ancestors to the pacenotesused in modern rallying. Juan Manuel Fangio was second in a sister car.

The 300 SLRs later scored additional world championship victories in the Tourist Trophy at Dundrod and at the Targa Florio in Sicily (both again 1-2 victories), which resulted in Mercedes winning the1955 World Sportscar Championship. Further non-championship victories were also scored at the Nurburging in Germany and Kristianstad in Sweden.

However, these impressive victories were overshadowed when the 300 SLRs, leading the 1955 24 Hours of Le Mans, were withdrawn after the horrific accident involving the car driven by Pierre Levegh. 82 spectators, and one competitor - Levegh - lost their lives in what remains the highest-fatality accident in the history of motorsport. Aspects of the accident were directly related to the SLR's unusual design - even with the innovative air-brake, the drum brakes were not effective enough to stop Levegh ploughing into the back of an Austin-Healey, causing the car to become airborne. Worse, the ultra-lightweight Elektron bodywork's high magnesium content caused it to ignite in the ensuing fuel fire, causing significant injury and loss of life amongst spectators; the magnesium fire was exacerbated by the race fire crew's unpreparedness for it, as they initially tried to extinguish it with water (which only made it burn hotter.) Following this tragedy, Mercedes withdrew from competitive motorsport until the mid-1980s.

Moss looked back at the 300 SLR, and he referred to it as the "greatest sportscar ever built- really an unbelievable machine."

Mercedes-Benz 300 SLR Uhlenhaut Coupé

Of the nine W196s chassis built, one was destroyed in the Le Mans disaster. Prior to the accident Mercedes motorsport chief Rudolf Uhlenhaut had already ordered two to be set aside for modification into a sort of hybrid between the SLR and the SL, featuring a slightly widened version of the SLR's chassis with enclosed bodywork. The high sill beams of the spaceframe required the fitment of the same famous 'gull-wing' top-hinged doors of the other two types. For testing, and in preparation for a possible Mercedes participation in the 1956 race season, two road-legal SLRs were built. Due to Mercedes' planned withdrawal from competitive motorsport at the end of 1955, the programme was abandoned, leaving Uhlenhaut to use one of the cars as a company car. This prolonged road use required the fitting of an extra suitcase-sized muffler to the near-unsilenced exhaust pipes to avoid arrest for breach of the peace.

This Uhlenhaut Coupé was regarded as the world's fastest car in the 1950s, and it is rumoured that, running late for a meeting, Uhlenhaut exploited the unlimited autobahns to make today's two-and-a-half-hour journey from Munich to Stuttgart (approximately 137 miles/220 km) in just over an hour.The Uhlenhaut Coupe was road tested by the US magazine Motor Trend and by two English journalists from Automobile Revue at four o'clock in the morning on a closed section of motorway outside Munich. The latter wrote; "We are driving a car which barely takes a second to overtake the rest of the traffic and for which 120 mph on a quiet motorway is little more than walking pace. With its unflappable handling through corners, it treats the laws of centrifugal force with apparent disdain," after a total of more than 2,000 miles (3,200 km). His only regret was that this was a sports car "which we will never be able to buy and which the average driver would never buy anyway.".