Press Release
The Eight-Cylinder Formula 1 Engine
Development of racing sports cars was heavily influenced by the first Mercedes 300SL that lined up at the start of the Mille Miglia in 1952 as well as a road-going version that made its debut in February 1954.With striking gullwing doors and a lightweight but high-strength tubular steel frame supporting an aluminum body, this famous model provided the basic concept for a new racer. However, the 300SLR also stood out with a number of features very much its own, including a five-speed transmission, 16-inch wheels and larger brakes.
Above all, the racing sports car developed far greater power than the production SL. The 300SLR was fitted with essentially the same engine that powered the 1954 Formula 1 race car, an in-line eight-cylinder with direct injection and dual ignition. The "Monoposto" and "Stromlinie" open-top body variants of the W196 R Silver Arrow had chalked up numerous victories, including the French Grand Prix, the Nürburgring race, the Italian Grand Prix, the Avus race in Berlin and the Argentinean Grand Prix.
The displacement of the Formula 1 straight-eight engine was increased from 2.5 to 3.0 liters for use in the 300SLR racing sports car, which boosted output to about 310 horsepower at 7,400 rpm, depending on the intake manifold. Maximum torque of 234 lb.-ft. at 5,950 rpm provided majestic pulling power. The straight eight was front-mounted longitudinally at an angle of 33 degrees and supplied with a high-octane fuel mixture of 65 percent low-lead gasoline and 35 percent benzene. In some races, alcohol was also used to further push up performance. As a rule, the racing sports car roared off the starting line with 44 gallons of fuel and more than nine gallons of oil on board. However, Moss and Jenkinson began their assault on the 1955 Mille Miglia with as much as 70 gallons of fuel in the tank.
Mercedes-Benz 300SLR Sports Racing Car (W 196 S)
The Stuttgart-based engineers conducted rigorous tests to make sure the engine would last. First, it was put through its paces at race speed over a distance of more than 6,000 miles, then subjected to a 32-hour non-stop run on a test rig.
This exhaustive test program was a key element in preparing for endurance road races such as the Mille Miglia, Tourist Trophy and Targa Florio, where reliability and durability was even more important than raw speed. The experience gained from pre-season testing paid dividends for the Mercedes team and helped earn the 300SLR a formidable reputation: the Silver Arrow engine, chassis and bodywork proved virtually indestructible.
"The car's powers of endurance are quite unbelievable," exclaimed Peter Collins in October 1955 after claiming victory in the Targa Florio. "This is a highly developed racing machine which also happens to be built like a tank, only with the lightning reactions of a wild cat. It is a truly magnificent feat of automotive construction."
An Engineer with Gasoline in his Blood
Rudolf Uhlenhaut was the technical brains behind the development of the 300SL and the 300SLR racing sports cars. Born in London on July 15, 1906 and the son of a German banker, he began his career in the testing department at Daimler-Benz in 1931, becoming technical director of the racing department in 1936 and senior engineer in charge of passenger-car testing in 1949. Uhlenhaut was a skilled driver as well as a talented engineer. For example, during chassis testing with the Formula 1 racing car at Hockenheim in 1954, he bettered Fangio's best time by 3.5 seconds! However, he never really considered driving in the races himself, preferring instead to direct operations from behind the scenes.Uhlenhaut frequently displayed a talent for improvisation. For example, during the 1955 Buenos Aires race, Stirling Moss complained that excessive force was required to brake effectively in his W196. Uhlenhaut got down on his hands and knees underneath a service truck, plucked out its brake booster unit and promptly fitted it into the W196.
High-Strength Filigree under the Skin
When the decision was made in 1951 to build a new Mercedes-Benz sports car, Rudolf Uhlenhaut was there to give the project - known by the abbreviation SL for "sport" and "light" - the necessary impetus. His was the engineering mind behind its space frame, made by welding together filigreed steel sections to support the engine, transmission and axles. Uhlenhaut, who had already played a major role in the success of the Silver Arrows between 1937 and 1939, designed a post-war series of smaller racing cars with rear-mounted engines in which he incorporated a wide tubular frame with a center section that formed a high-strength triangle in front of the cockpit.However, the "three-dimensional tubular steel frame" required more room underneath the doors than earlier designs, which meant that the door sills had to be moved up, ruling out the use of conventional doors. As a result, the team simply mounted the hinges to the roof, allowing the doors to open upwards instead of to the side, and the legendary gullwing doors were born. Rudolf Uhlenhaut used this same design for the 300SLR frame, as it had proved to be not only rigid and stable, but also extremely light. The tubular steel frame weighed only 110 pounds. While the engine alone accounted for 514 pounds, the 1955 Mille Miglia version of the SLR tipped the scales at less than 2,000 pounds.
To keep the hood as low as possible, the straight-eight engine was mounted at a 33-degree angle. However, the driveshaft then ran from the clutch at an angle under the driver's seat to the transmission, which was located behind the rear axle. As a result, the driver had to straddle the driveshaft tunnel, operating the clutch pedal on the left, the accelerator and brakes on the right!
An Air Brake is Developed For the 300SLR
Mercedes-Benz started the Le Mans 24-hour race in June 1955 with an ingenious piece of technology in tow: an air brake fitted to the rear of the 300SLR could be raised by a hydraulic pump. With a surface area of 7.5 square feet, the light-alloy wing had a significant braking effect as well as enhancing the car's cornering ability.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 conventional brakes and tires during long-distance races such as Le Mans and Reims. Neubauer wanted to use wind resistance to slow the car in particular at Le Mans, as the French track forced drivers to use the brakes hard and often to bring the car down from its maximum speed to as little as 25 mph. Although Mercedes-Benz enjoyed considerable on-track success in 1955, its winning run was overshadowed mid-season by a tragic accident during the Le Mans 24-hour race. Forced off the track as it approached the pit lane, one of the 300SLR racing sports cars was unable to stop and careered into a spectator grandstand. In all, 82 people were killed in what was clearly an appalling disaster. Although they were leading, the Mercedes team called all of its cars into the pits and retired them from the race.
"Uhlenhaut Coupe" Becomes the Fastest Sports Car of its Time
The SLR racing sports cars lined up again for the next major race of the 1955 season, the Swedish Grand Prix, and the eye-catching air brake was to prove its value once again. Juan Manuel Fangio took the checkered flag with an average speed of 100 miles per hour.Rudolf Uhlenhaut's new "company car," which he appeared in for the first time at the Swedish Formula 1 circuit, provided a fascinating side-show to the race itself. Spurred on by Mercedes' success in 1955, the Stuttgart engineer had spent time between races mulling over the idea of fitting the open 300SLR racing sports car with an enclosed cockpit for future endurance events.
Uhlenhaut's new coupe recorded a speed of 180 mph during a test conducted by "Automobil Revue" magazine at four o'clock in the morning on a closed section of motorway outside Munich. "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," scribbled the lucky test reporter after a total of more than 2,000 miles. 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." Only two examples of the SLR coupe were ever built.
For the SLR coupe's bodywork, the Mercedes engineers used ‘Elektron', an easy-to-work magnesium alloy which is even lighter than aluminum. The cabin resembled an aircraft cockpit, and the curved windshield generated little wind resistance. As in the 300SLR racing sports car, the engine in the "Uhlenhaut Coupe" was angled, and again, the driver had to control the pedals with his legs apart. The massive brake drums on the driven axles were moved inboard, to reduce unsprung weight and improve handling.
For anyone not already in the know, opening the boot lid was something of a mystery, with the inconspicuous "D" (for Germany) sign serving as the release lever.
Rudolf Uhlenhaut later called the SLR coupe "the fastest ‘company car' the company has ever built." The coupe attracted attention wherever it went, thanks to its standing not only as the fastest car registered for road use but also, one can assume, the loudest.
As a result, the police were only willing to grant it a license for road use if Uhlenhaut agreed to fit a muffler to the two exhaust pipes whenever he took the car out in public. Although the part in question - which was about the size of a suitcase - had the desired muffling effect, it jutted out noticeably from the right-hand side of the car and looked unwieldy. This could be the reason why old photos of the "Uhlenhaut Coupe" tend to show the left-hand side of the car. No matter, the excitement surrounding the car remained unaffected.
In 1959 Uhlenhaut took over as the head of passenger-car development at Mercedes-Benz and continued to define the technology and character of the brand's cars until his retirement in 1972. Rudolf Uhlenhaut died on May 8, 1989 just short of his 83rd birthday.
As the technical inspiration behind the Formula 1 Silver Arrows and the SLR racing sports car, as well as the creator of the 300SL Gullwing, Uhlenhaut left a legacy of very special cars. The "Uhlenhaut Coupe" of 1955 was without doubt one of the most outstanding super sports cars ever produced. For experts and motor racing enthusiasts alike, its name is synonymous with all-round technical genius, driving pleasure and reliability.
A Farewell to Motorsports
Uhlenhaut's plans to build on the success of the 300SLR in 1955 with the coupe version the following year were sidelined: in October 1955, shortly after Stirling Moss/Peter Collins and Juan Manuel Fangio/Karl Kling had completed a one-two victory in the season-ending Targa Florio, the Daimler-Benz board of management decided to withdraw from motor racing. The Mexican government had cancelled the 1956 Carrera Panamericana for safety reasons, and the shock of the Le Mans tragedy of June 11, 1955 was still very keenly felt. A period of reflection away from motorsports appeared to be the best move at the time. Nobody could have imagined that it would be decades before Mercedes made a return to the track.
