One and Done - a Historical & Technical Appraisal of the Mercedes-Benz W196S 300 SLR
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BACKGROUND
Following a 13 year absence, Mercedes-Benz returned to motor racing in 1952 with the W194 300 SL.
A three-litre straight six-powered Sports Prototype, the W194 proved an enormous success, winning four of the five races it contested during 1952 to include the Le Mans 24 Hours and Carrera Panamericana. Only the Mille Miglia (where the W194s placed second and fourth) failed to yield victory.
At the time, Mercedes had chosen to re-enter Sports car racing as opposed to F1 because Formula 1 was organised to Formula 2 regulations and the two-litre un-supercharged engine limit did not meet the firm’s technical aspirations.
However, it was announced ahead of time that, for 1954, proper Formula 1 regulations were to be reinstated with a 2.5-litre un-supercharged engine limit.
With this in mind, Mercedes-Benz abandoned any notion of a 1953 competition programme with the W194 300 SL and focused their attention on developing a suitable F1 challenger.
The resultant W196 arrived at the 1954 French Grand Prix.
Following his switch from Maserati, Mercedes driver, Juan Manuel Fangio, won four of the remaining six F1 races in 1954 driving a W196.
1955 would see Mercedes expand their motor sport activities beyond F1 to include an attack on the World Sportscar Championship. The six round contest comprised endurance events in Argentina, the USA, France, Great Britain and a brace of Italian road races.
Mercedes would participate from round three onwards taking in the Mille Miglia, Le Mans 24 Hours, Dundrod Tourist Trophy and Targa Florio. Outside of the championship, they would also compete in the domestic Nurburgring Eifelrennen and the Swedish Grand Prix.
Competition for the new W196S 300 SLR was expected to be fierce. In addition to Scuderia Ferrari, Mercedes would be up against works teams from Jaguar, Maserati, Aston Martin and Gordini.
For the task, Mercedes essentially created a Formula 1 car with two-seat fully enveloped bodywork.
Testing began in secret during late 1954.
The new car was spotted in early April 1955 as Mercedes conducted a series of tests on Italian soil to prepare for the Mille Miglia. It was at the Mille Miglia (which started on April 30th) where the 300 SLR made its official public debut.
CHASSIS
The chassis was a welded aluminium tubular spaceframe.
Compared to the W196 F1 car, it had modified two abreast seating and a wheelbase extended from 2210mm to 2370mm. Rear track was widened by 22mm. A 155-litre fuel tank was installed behind the back axle.
Front suspension was via double wishbones and torsion bars. At the rear, Mercedes used a single-joint swing axle with longitudinal torsion bars. Telescopic shocks were fitted all round.
The drum brakes had a 350mm diameter at the front and 275mm diameter at the rear. Each axle ran off its own hydraulic system. As the drums were too large to fit within the SLR’s 16-inch diameter wheels, they were mounted inboard at either end.
The wire wheels were 6 and 7-inches wide front to rear.
ENGINE / TRANSMISSION
Compared to the W196 Grand Prix racer, the W196S 300 SLR received a bigger engine as, unlike F1, the World Sportscar Championship did not impose any limit on displacement.
The resultant Type M196S straight six was a long stroke version of the F1 powerplant.
By extending the stroke from 68.8mm to 78mm (which matched the bore dimensions) capacity rose from 2496cc to 2982cc.
As the sports car engine would have to run for considerably longer than the F1 variant, compression was dropped from 12.0:1 to 9.0:1.
To reduce crank flexing, power take-off was from the centre of the engine via a gear rather than the end of the crankshaft.
Otherwise, the two motors were largely similar.
The engine block was formed from Silumin lightweight alloy as was the twin cam head with its desmodromic valve gear.
Ignition was via two spark plugs per cylinder and a pair of high voltage Bosch magnetos. Bosch also supplied the mechanical fuel-injection system.
Other equipment included a ten roller bearing crankshaft and dry-sump lubrication.
The engine was front longitudinally mounted and canted at 53° to the right.
As opposed to special methanol-based racing fuel used by the F1 car, the 300 SLR ran on 65% low lead and 35% benzene.
Whereas the smaller, more highly stressed F1 engine produced 290bhp at 8500rpm, the 300 SLR developed 310bhp at 7400rpm. Its torque rating was 235lb-ft at 5950rpm.
Transmission was through a five-speed gearbox with dry single-plate clutch mounted in unit with the differential behind the rear axle.
BODYWORK
With its flowing lines, perfect proportions and elegant details, the 300 SLR was arguably the most handsome Sports Prototype of its era.
The bodywork was fashioned from ultra-light Elektron magnesium alloy.
The primary intake was flanked by shapely front fenders with covered headlights. A secondary duct was carved from the enormous front hood.
Two large vents were located down each flank. On the passenger side, they were used as exit points for the megaphone exhausts.
As per the regulations, the 300 SLR came with full complement of lighting and also carried a spare wheel (or two).
At the back of the car was an aerodynamically formed head rest, a duplicate of which could be added if a navigator was on hand. Should a navigator not be required, a rigid body coloured tonneau was usually fastened above the passenger seat.
INTERIOR
Bucket seats were trimmed with tartan fabric inlays and blue vinyl bolsters to match the sills.
The drilled metal dash was body coloured. It housed a detachable three or four-spoke wood-rimmed steering wheel and gauges for engine speed, oil pressure and water temperature.
All nine 300 SLRs were left-hand drive with a centrally located open-gate gearchange.
WEIGHT / PERFORMANCE
Weight was a quoted 900kg.
With a power-to-weight-ratio approaching 350bhp per ton, the SLR could top 180mph and sprint from 0-62mph in under five seconds.
PRODUCTION CHANGES - AIR BRAKE
Mercedes created a sensation in June 1955 when at Le Mans with all its SLRs featuring massive air brakes designed to reduce wear on the rear brakes and tyres. The air brake consisted of a hinged flap operated by hydraulic rams controlled from a lever on the dash. It automatically lowered again when second gear was subsequently engaged. All three cars were equipped as such.
SLR COUPE
After Mercedes’ first race of 1955, the thousand-mile Mille Miglia round Italy road race won by Stirling Moss in a W196S, Mercedes commissioned an SLR Coupe for endurance racing. A pair of cars was ordered by chief engineer, Rudolf Uhlenhaut, who expected them to be ready in August so they could race in the end-of-season Carrera Panamericana.
In its transformation to Fixed Head trim, the SLR gained an enclosed Fastback cabin with panoramic wraparound front and rear screens. Neatly integrated to the elegant, tightly packaged canopy were two Gullwing doors, each connected with a pair roof-mounted struts. For ventilation, the rear section of the side window could be slid forwards.
All in all, the cleaner aerodynamics of the SLR Coupe was expected to yield another 10mph or so in Mercedes’ top speed war with Ferrari and Jaguar.
PRODUCTION
In total, Mercedes built eight copies of the W196S 300 SLR.
The first, chassis number 0001/54, was followed by cars numbered chassis 0002/55 though 0008/55.
The first SLR Coupe (chassis 0007/55) started life as the SLR Spyder raced by Fangio and Moss at the 1955 Le Mans 24 Hours. Chassis 0007/55 made its debut appearance in SLR Coupe trim when it served as T-car for the Swedish Grand Prix at Kristianstad (August 7th). Production of the second SLR Coupe (chassis 0008/55) started in December 1955, long after Mercedes had quit motor racing. This car was completed in June 1956.
COMPETITION HISTORY – EARLY SEASON
Mercedes made a big splash for the 300 SLR’s debut with a four-car Mille Miglia entry (April 30th-May 1st).
While two of the SLRs crashed out along the tortuous 992 mile loop from Brescia to Rome and back, the Mercedes entries of Stirling Moss / Denis Jenkinson and Juan Manuel Fangio (driving solo) finished first and second overall.
Moss and Jenkinson broke almost every available record, finishing 22 minutes clear of Fangio whose car was suffering intermittent fuel-injection trouble. Third place went to the works Ferrari 118 LM of Umberto Maglioli and Luciano Monteferrario which finished a further 13 minutes back.
Four weeks after its successful Mille Miglia outing, Mercedes entered a three car team of SLRs for the 228km Nurburgring Eifelrennen (May 29th) which, at the time, was Germany’s biggest sports car race.
Tellingly, the SLRs streaked away and proved unbeatable. By half distance, the trio of silver cars led Giuseppe Farina’s works Ferrari by three minutes. As per team orders, Moss allowed Fangio to take the lead late on and the Argentine won by a tenth of a second. Having run third, Kling’s SLR developed valve gear trouble on lap eight and was overtaken by Masten Gregory’s Ferrari 750 Monza which bagged the final podium spot. Kling placed fourth.
At the Le Mans 24 Hours two weeks later (June 11th-12th), Mercedes entered a team of three air brake-equipped SLRs.
After the Mercedes drivers had eased themselves into the race, the order two hours in was Hawthorn (Jaguar), Fangio (Mercedes), Castellotti (Ferrari), Maglioli (Ferrari), Kling (Mercedes) and Levegh (Mercedes).
At half-past two, tragedy occurred.
1955 LE MANS DISASTER
Heading down the pit straight, Hawthorn pulled his Jaguar to the right-hand side of the track and started to brake for his pit stop in front of Austin-Healey driver, Lance Macklin. Macklin swerved out from behind the slowing Jaguar straight into the path of Levegh’s SLR.
Levegh ploughed into the back of Macklin’s car which acted as a ramp and launched the Mercedes into the air. The SLR skipped over a protective earth bank at 125mph and barrel rolled into the crowd. Levegh was thrown from the car and fatally fractured his skull.
83 spectators were killed in what remains motor racing’s most catastrophic crash.
Ultimately, Mercedes withdrew both its remaining cars from the race shortly before 2am, by which time the scale of Levegh’s accident had become clearer. At the time, the Fangio / Moss SLR had a two lap lead over the second place Jaguar.
FALLOUT
Following the Le Mans disaster, a whole raft of events were cancelled to include the notoriously dangerous Carrera Panamericana road race through Mexico.
Mercedes decided they would abandon motor sport at the end of the 1955 season.
COMPETITION HISTORY – LATER SEASON
The SLRs were wheeled out for three subsequent appearances: the Swedish Grand Prix at Kristianstad (August 7th), the Dundrod Tourist Troph in Northern Ireland and the Sicilian Targa Florio. The TT and Targa were rounds five and six of the World Sportscar Championship; if Mercedes could do well, there was still a chance it could snatch the World title from Ferrari.
Against a small but high quality field on the new Rabelov circuit in Kristianstad, the two-car SLR entry put on a demonstration of high speed reliability with Moss invariably a yard or so behind Fangio in his customary role as shadow to the F1 world champion. Castellotti’s Ferrari eventually finished third, 90 seconds behind the two Mercedes.
Things could not have gone much better at the Dundrod Tourist Trophy road race in Belfast where Moss / Fitch led a Mercedes 1-2-3 with Fangio / Kling second and von Trips / Simon third.
Going into the final World Sportscar Championship event, the Targa Florio, Ferrari led with 19 points, Mercedes and Jaguar were level on 16 points and Maserati were fourth on 13 points.
Both Maserati and Ferrari would have to drop a couple of points if they did well in Sicily as only a manufacturer’s best four results of the year counted towards its final points tally.
Jaguar would certainly not win the title as they didn’t attend.
After a topsy turvy 13 laps of the 72km Little Madonie circuit, Moss and Peter Collins put on one of the greatest drives ever seen in a motor race to win by nearly five minutes from team-mates Fangio / Kling.
It had looked as though Ferrari had been set to scoop second place (and with it the 1955 title), but in a dreadful tactical error, the Italian team was forced to bring their second-placed driver into the pits for an extra stop as he had already covered the maximum six laps permitted.
This oversight promoted the Fangio / Kling SLR to second and handed Mercedes the championship by 24 points to Ferrari’s 22.
Text copyright: Supercar Nostalgia
Photo copyright: Mercedes-Benz - https://www.mercedes-benz.com
