Mercedes-Benz 300 SLR — BrandWiki

Mercedes-Benz 300 SLR

car name	Mercedes-Benz 300 SLR
category	World Sportscar Championship
constructor	Daimler-Benz AG
team	Mercedes-Benz
drivers	🇦🇷 Juan Manuel Fangio 🇬🇧 Stirling Moss 🇫🇷 Pierre Levegh
engine name	Mercedes-Benz M 196 S
configuration	straight-8
capacity	2982 cc
turbo/na	naturally aspirated
engine position	front-mid
gearbox name	Daimler-Benz
type	5-speed transaxle gearbox
front suspension	Double wishbone, torsion bar springs, telescopic shock absorbers
rear suspension	Single-joint swing axle, longitudinal torsion-bar springs, telescopic shock absorbers
fuel	Super petrol (98 RON)
tyres	Continental
debut	1955 Mille Miglia
designer	Rudolf Uhlenhaut

The Mercedes-Benz 300 SLR (W 196 S) is a two-seat sports racing car that took part in the 1955 World Sportscar Championship before a catastrophic crash and fire at Le Mans later that year ended its domination prematurely. The car was designated "SL-R" (for Sport, Leicht, Rennen, eng: sport, light, racing), which was later condensed to "SLR". Technically, the W 196 S is based on the W 196 R, but has a slightly different engine, displacing 3 litres.

Just as the W 196 R Formula One racer's M 196 R engine, the 300 SLR's M 196 S engine is a direct-injected 3-litre straight-eight engine (but with a 78 mm bore and stroke); its rated power is 302 PS.[1]

The W 196 S's monoposto driving position was modified to standard two-abreast seating, headlights were added, and a few other changes made to adapt a strictly track competitor to a 24-hour road/track sports racer.

Hall of Fame Formula One driver and former Mercedes-Benz team 300 SLR race driver Stirling Moss described the 300 SLR as "The greatest sports racing car ever built – really an unbelievable machine."[2]

Two of the nine 300 SLR rolling chassis produced (nicknamed the "Uhlenhaut Coupé

History

Name

In spite of its name and strong resemblance to both the streamlined 1952 W194 Le Mans racer, and the iconic 1954 300SL Gullwing road car it spawned, 1955 300 SLR was not derived from either. Instead, it was based on the successful 2.5-litre straight-eight-powered 1954–1955 Mercedes-Benz W196 Formula One champion, with the engine enlarged to 3.0 litres for the sports car racing circuit and designated "SL-R" for Sport Leicht-Rennen (eng: Sport Light-Racing). All were the work of Daimler-Benz's design chief Rudolf Uhlenhaut.

Racing record

In the 1955 World Sportscar Championship, only the best 4 results out of the 6 races would count, and most factory teams skipped the early overseas events. So did Mercedes as a Sports Car team, but not as a F1 team. The 16 January 1955 Argentine Grand Prix was won by defending World Champion Juan Manuel Fangio for Mercedes, suffering burns to his leg. As the new 300 SLR sports car was not ready yet, its enlarged 3 litre straight-8 pump gas engine would be fitted into the single seater Mercedes-Benz W196 Formula 1 cars for the 30 January 1955 Buenos Aires Grand Prix Formula Libre race that was won by Fangio ahead of Moss.

In between, the 1955 1000 km Buenos Aires was won 1-2 by local Argentinians for Ferrari after the works entries were disqualified, and the Maserati in 3rd place won 4 points for the brand. The new 300 SLR was not yet ready for the 1955 12 Hours of Sebring in March which was mainly contested by Americans. After some controversy, a factory Jaguar won ahead of private Ferrari and Maserati.

After intense preparation of the Mercedes team for the 1955 Mille Miglia, driving the public roads several times, Mercedes team driver Stirling Moss won the 1955 Mille Miglia in a 300 SLR, setting the event record at an average of 157.650 km/h over 1600 km. He was assisted by co-driver Denis Jenkinson, a British motor-racing journalist, who informed him with previously taken notes, ancestors to the pacenotes used in modern rallying. Teammate Juan Manuel Fangio was second in a sister car.

The horrific 1955 Le Mans disaster overshadowed the 1955 24 Hours of Le Mans for which innovative wind-brakes were added to reduce fading of the inboard drum brakes. The third Mercedes driven by Pierre Levegh got involved when the first pit stops were made by Jaguar, causing an Austin-Healey to make an evasive move, and Levegh could not prevent rear-ending the Austin-Healey coming into his way, launching his car into the air. Upon impact, the ultra-lightweight Elektron bodywork's high magnesium content caused it to ignite and burn in the ensuing fuel fire. Compounding it, an uninformed race fire crew initially tried to extinguish the fire with water, only making it burn hotter. Eighty-three spectators and Levegh lost their lives in what remains the highest-fatality accident in the history of motorsport. The leading 300 SLRs were withdrawn at night.

Due to many races getting cancelled in summer of 1955, and a three month summer break in the 1955 World Sportscar Championship season, Mercedes entered non-championship sportscar races, and scored wins at the Eifelrennen in Germany and the 1955 Swedish Grand Prix.

The 300 SLRs scored a decisive 1–2–3 finish in the Tourist Trophy at Dundrod, Ireland. This was only the second win, but denied 2nd and 3rd place points to the competition, and opened up the opportunity to win the championship in Sicily, as the 1955 Targa Florio replaced the cancelled Carrera Panamerica and was run in October, not as usual in May, as a one-off second Italian WC round only in 1955. Some years later, the Targa replaced the Mille Miglia.

After some more intense practise on the island, the factory drivers learned the challenging course. They scored another 1–2 at the 1955 Targa Florio, which earned Mercedes the WC victory with two points ahead of Ferrari.

In total, the 300 SLR had an impressive record as it won five races and was withdrawn while leading one.[4]

As decided earlier, Mercedes terminated its motorsport programme at the end of the 1955 season, having proven that it could win in two categories. The company would stay away from major racing for the next three decades, concentrating on road cars, new factories etc.

Uhlenhaut Coupé

Daimler-Benz made two road-legal 300 SLR coupés, known today as Uhlenhaut Coupé. One of these two cars once served as the personal car of its designer, Daimler-Benz motorsport chief Rudolf Uhlenhaut, hence the name.

Prior to the Le Mans accident he had ordered two of the nine W196 chassis built to be set aside for modification into an SLR/SL hybrid. The resulting coupé featured a significantly more sculpted body than the 300 SL fitted over a slightly widened version of the SLR's chassis, with signature gull-wing doors still needed to clear its spaceframe's high sill beams. These were intended to race in the Carrera Panamericana which was cancelled because of safety concerns following the Le Mans disaster.

Before the project could be seen through, however, Mercedes announced a planned withdrawal from competitive motorsport at the end of 1955, in the works even before Le Mans. The hybrid program was abandoned, leaving Uhlenhaut to appropriate one of the leftover mules as a company car with only a large suitcase-sized muffler added to dampen its near-unsilenced exhaust pipes.

With a maximum speed approaching 290 km/h (180 mph),[5] the 300 SLR Uhlenhaut Coupé easily earned the reputation of being the era's fastest road car. A story circulates that, running late for a meeting, Uhlenhaut drove up the autobahn from Munich to Stuttgart in just over an hour, a 220 km journey that today takes two-and-a-half hours.[6]

Technical description

Design

The 300 SLR was front mid-engined, with its long longitudinally mounted engine placed just behind the front axle to better balance front/rear weight distribution. A brazed steel tube spaceframe chassis carried ultra-light Elektron magnesium-alloy bodywork (having a relative density of 1.8, less than a quarter of iron's 7.8), which contributed substantially to the low vehicle mass of 901 kg for the roadster,[10] 1117 kg in the case of the coupé.

The SLR had a second seat for a co-driver, mechanic, or navigator, depending on the race. As it turned out, this was only needed during the Mille Miglia, as the 1955 Carrera Panamericana was cancelled due to the 1955 Le Mans accident. On some circuits such as the Targa Florio the extra seat was covered and passenger windshield removed to improve aerodynamics. The front windshield for the two-seater mode was originally steeply raked, but due to intense turbulence in the cabin this was redesigned repeatedly during testing at Hockenheim before Mille Miglia. Jenkinson used the long curls of his trademark beard as flow visualisation aids. Thus evaluated, the final design used at Mille Miglia ended up being near vertical.[11]

A total of nine W 196 S chassis were built: seven roadsters, and two coupés. Work was ongoing on an updated design for 1956 when Mercedes-Benz abruptly announced their withdrawal from all forms of motorsport following the Le Mans tragedy. The front suspension, the engine, and the brakes were being redesigned for this cancelled project; in parallel with the Uhlenhaut Coupés a coupé version had also been under development, with the aim of once again winning the Carrera Panamericana.[4]

Engine

The M 196 S engine is a naturally aspirated straight-eight engine with a bore and stroke of 78.0 mm, resulting in a displacement of 2982 cc. The engine has a peak power output of 310 PS at 7400 rpm, with maximum sustained power of 276 PS at 7000 rpm.[12] Its maximum torque is 31.7 kpm at 5950 rpm, giving the engine a very high BMEP of 1.31 MPa. Like in the W 196 R, the engine was canted to the right at 53 degrees to lower the car's profile, resulting in slicker aerodynamics and a distinctive bulge on the passenger side of the hood shared with the streamlined Type Monza Formula one car. To reduce crankshaft torsion, power takeoff was from the centre of the engine via a gear rather than at the end of the crankshaft. Daimler-Benz fitted the engine with a single desmodromic intake valve, and a single desmodromic exhaust valve per cylinder, actuated by two spur-gear driven overhead camshafts. The fuel system is a direct fuel injection system with a mechanically driven eight-plunger inline injection pump made by Bosch. In addition to that, the W 196 S's engine was fitted with a dry-sump lubrication system and chromium-coated aluminium cylinder sleeves. For ignition, the engine was equipped with conventional double magnetos.[12] Unlike the M 196 R engine, the M 196 S engine is designed to run on standardised, commercially available Super 98 RON petrol (DIN 51600).[1]

Suspension system

To enhance stopping power extra wide diameter drum brakes too large to fit inside 16" wheel rims were used, mounted inboard with short half shafts and two universal joints per wheel. Suspension was four-wheel independent. Torsion bars fitted inside the frame's tubes were used in the double wishbone front. To prevent cornering forces from raising the car, as occurs with short swing axles, the rear used a low-roll centre system featuring off-centred beams spanning from each hub to the opposite side of the chassis crossing one-another over the centreline. Nevertheless, snap-oversteer could be still a notable problem at speed.

At Le Mans in 1955, the 300 SLRs were also equipped with a large rear mounted "wind brake" that hinged up above the rear deck to slow the cars at the end of the fast straights. The idea came from director of motorsports Alfred Neubauer, who had been seeking to reduce wear on the huge drum brakes and tyres during long-distance endurance races where cars repeatedly had to decelerate from 180 mi/h to as little as 25 mph.[7] In tests the 0.7 m2 light-alloy spoiler slowed the car dramatically and improved cornering, helping to compensate for the superior new disc brakes of the SLR's main rival Jaguar D-type.