This Is Why The Mercedes-Benz 300 SLR Is Unbeaten

Photography from Daimler via Mercedes-Benz Classic Centre

It’s both difficult to put a classic race car into a modern context and to talk about such weapons-grade machinery without delving into the small engineering details that make it great. Sometimes, however, a car requires your undivided attention.

Its racing achievements are stuff of legend, and listed here. But first, why is this car so special?

The Man: Rudolf Uhlenhaut

First, you must understand that Mercedes-Benz employed a brilliant engineer in its racing department, joining the company in 1931. Rudolf Uhlenhaut’s name is forever attached to this car because of a unique set of circumstances that made him the ideal person to create such a machine.

After just five years, he was made the leader of the racing department and a year into his tenure had turned around Mercedes-Benz’ Grand Prix fortunes by winning the World Championship in 1937. Daimler itself says that during those early years in the racing department, Uhlenhaut took it upon himself to learn how to drive and understand the company’s fastest machines.

Even though he is said to have been, eventually, as fast as Juan Manuel Fangio under certain conditions, Uhlenhaut was too precious an engineer to the company to be allowed to race because of the risks involved. Instead, he honed his skills on the fast, winding, sweeping roads around Stuttgart, Germany—his personal transportation was a version of the 300 SLR widely regarded as the fastest road car of the era.

Why is it important that a fast, talented engineer was forced to hone his craft on, often, public roads? Because the Mille Miglia, the car’s greatest success, was one long open road course. Even today, Sir Stirling Moss says, “The fact the car’s really old doesn’t matter—that car, the way it is now, I reckon we’d beat any other cars, anyway!”

The Machine: Mercedes-Benz 300 SLR #722

There were a number of different body styles, and even though many of them appear outwardly to resemble the road-going 300 SL Coupé and Roadster, the SLR is a much different car.

Based on the company’s single seat championship-winning W196 Grand Prix car, the SLR actually enjoyed more power thanks to, often, fewer restrictions in sports car regulations. In modern terms, it would be like taking Lewis Hamilton’s Formula 1 car from the grid, adding another seat, and letting it loose.

This means, it has two more cylinders than the road-going 300 SL models for a total of eight, arranged in a “straight” configuration in the middle of the car but canted to the right at a slight 33-degrees in order to improve aerodynamics. Like modern supercars, the engine was mounted behind the front axle, giving it a ‘front-mid’ layout. “Hot rodding” an engine in the aftermath of the Second World War means, well, borrowing technology used on fighter planes. In this case, the car ran a direct (!) fuel injection system inspired by the one fitted to the Messerschmitt Bf 109E.

Bodywork was made from Electron, a magnesium alloy that was—if you don’t have carbon fibre around—one of the lightest ways to skin a race car with metal. The car enjoyed an aluminum chassis, and hit circuits with a weight of around 1,940 lbs (880 kg)—lighter than the modern-day Lotus Elise.

The Achievement: 1955 Mille Miglia

Power and light weight will get you most of the way to the winner’s circle, and the SLR was a strong car by any measure. But in our estimation, it was the unique “feel” for how a high-performance car could be adapted for the open road that only Uhlenhaut could have used to tune the car for gruelling races like the Mille Miglia.

At the start of the 1955 Mille Miglia race, Stirling Moss and co-driver Denis Jenkinson had 70 U.S. gallons (265 litres) of fuel on board the car for its attempt at the 1000-mile race. Only a design that respects the undulating and unforgiving attributes of winding public roads would be able to carry that much extra weight and still perform at speeds in excess of 150 mph (240 km/h).

It’s why we can say that in May, 1955, at Italy’s Mille Miglia, the Mercedes-Benz 300 SLR was unbeaten. Stirling Moss’ average speed of nearly 100 mph (160 km/h) over ten hours of non-stop driving was a herculean feat, and one of those moments in sport when a number of factors came together to produce an unforgettable achievement.

Racing success

Winner, 1955 World Sportscar Championship

Winner, 1955 Mille Miglia, Brescia-Rome, Italy (Moss/Jenkinson)

Winner, 1955 RAC Tourist Trophy, Dundrod Circuit, Ireland (Moss/Fitch)

Winner, 1955 Targa Florio, Circuito delle Madonie Piccolo, Italy (Moss/Collins)

Winner, 1955 Swedish Grand Prix, Kristianstad, Sweden (Juan Manuel Fangio)

Winner, 1955 ADAC-Eifel-Rennen, Nürburgring, Germany (Juan Manuel Fangio)