1934: Birth of a new star – the W 25
Circuit races and speed records
432.7 km/h – still the fastest speed ever recorded on a public highway
1932 hardly provided a favourable backdrop for motor sport in Germany, with unemployment, the economic depression and the closure of the Mercedes-Benz works racing department. There were good prospects for the future, however, for in autumn the AIACR (Association Internationale des Automobile Clubs Reconnus) in Paris announced a new formula for Grand Prix racing that was to come into force in 1934. The new rules stipulated a maximum weight of 750 kilograms without fuel, oil, coolant and tyres, but otherwise no restrictions for constructors. This was an ideal opportunity for Mercedes-Benz to compete with a new car. The SSKL was now a representative of a bygone age. Its weight alone was enough to bar any possibility of adaptation for the new rules, at almost double the new maximum figure.
Mercedes-Benz made the decision to develop a new racing car in 1933, following sustained pressure for a return to the race track from racing manager Alfred Neubauer. Furthermore, the whole motor sport context in Germany had now changed with the seizure of power by the National Socialists: the new government’s commitment to the rapid development of the automotive industry led it to continue existing autobahn construction projects, lower the tax on new cars, and encourage leading automakers to get involved in motor sport. These policies also gave rise to a new competitor for Mercedes-Benz: the Chemnitz-based Auto Union, created in August 1932 as a result of the merger between four Saxony-based motor vehicle manufacturers: Audi, DKW, Horch and Wanderer. The rivalry between the racing cars with the three-pointed star and those with the four rings was to shape European racing history in the years up to 1939.
One of the first drivers contacted by Neubauer was Rudolf Caracciola – in spite of the months he had spent in hospital with serious leg injuries following an accident in Monaco in April 1933, and doubts that he would be fully fit to race again. The other team members were Manfred von Brauchitsch, Luigi Fagioli, Hanns Geier and Ernst Henne. By the winter of 1933, Neubauer was enthusing about an elegant monoposto designed to carry its team once more to victory.
A team of engineers led by the head of the principal design office, Hans Nibel, were working under intense time pressure on the development of the new car. The front engine design may have been rather conservative in comparison with Auto Union’s mid-engine car and the company’s own earlier designs such as the Benz ‘Teardrop car’, but the combination of a slim body, mechanically supercharged 3.4-litre in-line eight-cylinder engine, individual wheel suspension and direct rear axle transmission was a recipe that would carry all before it on the race track. The chassis was the responsibility of Max Wagner, while the engine was the domain of Albert Heess and Otto Schilling. Meanwhile, in the research and development department under Fritz Nallinger, Georg Scheerer, who had also assisted at the birth of DMG’s supercharged car, was running exhaustive tests on the engine. Otto Weber assembled the engine and Jakob Kraus fitted the chassis, both having been part of the DMG sortie to Indianapolis in 1923.
Test drives of the new Mercedes-Benz monoposto started in February 1934 in Monza and on the motorway between Milan and Varese. The 235 kW car (later boosted to 260 kW with a new Esso fuel mixture) recorded maximum speeds of over 250 km/h.
Mercedes-Benz also decided on a new chassis colour for the W 25: silver. The debut of the new car had been planned for the Avus race in Berlin in May 1934, but the team withdrew at the last minute on account of technical problems. Accordingly, the new car made its first appearance one week later, at the International Eifel race at the Nürburgring on 3 June. The W 25 lined up at the start in silver – supposedly, as legend has it, after the cars on the Nürburgring had been stripped of their white paint for weight reasons. Even though this race was not run in accordance with the 750-kg formula, apparently the team was determined to present a car that met the new regulations. The name ‘Silver Arrow’ was coined some time later and gradually caught on over the years.
So the Eifel race in 1934 was the first start for the new Mercedes-Benz formula racing car – and also its first victory. Manfred von Brauchitsch finished first in his W 25 at an average speed of 122.5 km/h, setting a new track record in the process.
Further victories in the W 25’s first year included Caracciola winning the Klausen race, Luigi Fagioli’s triumph at the Coppa Acerbo around Pescara and a Mercedes-Benz victory in the Italian Grand Prix at Monza. A total of some 1300 corners and chicanes made Monza the most demanding event on the 1934 racing calendar. As a result of his accident, Rudolf Caracciola was still in severe pain and not fit enough to make it through the entire race. So halfway through the race Luigi Fagioli took over at the steering wheel of the car starting under the number 2. Technical problems with his own car had forced Fagioli out at an early stage of the race, but he successfully defended the lead Caracciola had built up over the field by that stage and was first across the finish. Fagioli also won the Spanish Grand Prix ahead of Caracciola and finished second in the Masaryk Grand Prix in Brno.
The results from the 1934 season clearly put Mercedes-Benz back at the top of the international motor sport ratings. Caracciola further underscored the performance of the new Grand Prix racer with a raft of records in the winter of 1934. In Gyön, near Budapest, he drove the Mercedes-Benz W 25 with fully enclosed cockpit – and therefore termed a ‘racing saloon’ – on a concrete track. He set an international speed record for Class C (displacement of 3 to 5 litres) for the flying kilometre and flying mile, with speeds of 317.5 km/h and 316.6 km/h respectively. He also set a new world record for the standing start one mile, at 188.6 km/h. In December, Caracciola then set an international Class C record of 311.9 km/h over 5 kilometres on the Avus track.
In the 1935 season, the Stuttgart company responded to the success of its redoubtable rivals at Auto Union with several enhancements to the W 25. The most powerful of the range of engines, the M 25 C, now developed 340 kW at 5800 rpm, with a displacement of 4310 cc. This car gave Mercedes-Benz almost total dominance of the 1935 racing season. Rudolf Caracciola was back at his best, and won the Tripoli Grand Prix, the Eifel race, the French Grand Prix, the Belgian Grand Prix, the Swiss Grand Prix and the Spanish Grand Prix. The title of European Champion, awarded that year for the first time, therefore went to the number one driver of the Silver Arrows. The 1935 season also included victories for Luigi Fagioli in the Monaco Grand Prix, the Avus race and the Grand Prix of Barcelona (ahead of Caracciola).
The 1936 version of the W 25, developing 330 kW and with a shorter wheelbase, was not however able to replicate this string of successes. The 1936 season brought only two Grand Prix victories for Mercedes-Benz, in Monaco and Tunis (both Caracciola).
1937: Year of the W 125
Following the disappointing performance of the modified W 25 in its third season, Mercedes-Benz developed a new car for the 1937 racing year, the last season under the existing formula rules. As a foretaste of the innovation capability of the racing department in Stuttgart, in November and December, Rudolf Caracciola broke five international records and one world record in a Mercedes-Benz 12-cylinder streamlined record car on the new autobahn between Frankfurt and Heidelberg, comfortably passing the marks set by Hans Stuck for Auto Union on the same stretch of road the previous March.
The 1937 racing year was dominated by the eight-cylinder W 125 monoposto. The engine again included a mechanical supercharger, developing over 441 kW from a displacement of 5.6 litres. The W 125 was designed by an engineer just 30 years of age, who took over the new racing department in mid-1936: Rudolf Uhlenhaut. As well as developing new design concepts, Uhlenhaut also put his racing cars to the test personally. He succeeded in putting Mercedes-Benz back at the top of the European motor racing scene. The design included numerous innovations in matters of detail. For example, for the first time in a Silver Arrow the supercharger was downstream from the carburettor, so it was the final mixture that was compressed. This in-line eight-cylinder unit was the most advanced version of the Grand Prix engine that had been used since the 1934 season.
The backbone of the car was an ultra-sturdy frame of special steel with four cross members. The front wheels were steered by double wishbones with helical springs, as in the celebrated 500 K and 540 K production models. The wheels at the rear were mounted on a De-Dion double-articulated axle providing constant camber adjustment, with longitudinal torsion springs and hydraulic lever-type shock absorbers. Overrun torque and braking torque were transferred to the chassis by lateral links.
After extensive test drives on the Nürburgring circuit, Uhlenhaut opted for a revolutionary chassis design. He made the bold and visionary decision to replace the customary principle of hard springs and minimum damping with the exact opposite. The W 125 featured soft-sprung suspension and exceptionally long spring travel, with a high level of damping, setting the pattern for today’s Mercedes-Benz sports cars. The external appearance of the car was very similar to its forerunner, the most distinctive feature of the W 125 being the three cooling openings at the front end. The car had free-standing wheels, with a streamlined chassis being used only for the very fast Avus race on 30 May 1937.
Success followed success during the 1937 season. Hermann Lang won the Tripoli Grand Prix, and also the Avus race, in an aerodynamically optimised W 125. His maximum speed of 271.7 km/h in that race was not bettered until 1959. Caracciola and von Brauchitsch finished in second and third places respectively in the Eifel race, and Caracciola claimed victory in the German Grand Prix ahead of von Brauchitsch. The latter took the Monaco Grand Prix ahead of Caracciola and Christian Kautz, with Goffredo Zehender in fifth place. The Swiss Grand Prix was a triple victory, with Caracciola, Lang and von Brauchitsch sharing the podium, and Caracciola finished first in the Italian Grand Prix ahead of Lang. Caracciola rounded off this record-breaking season with victory at the Masaryk Grand Prix in Brno ahead of von Brauchitsch. Despite driving a full complement of races for Auto Union, Bernd Rosemeyer was able to take only four wins. The superiority of the Mercedes-Benz team was also clearly illustrated by its drivers taking the first four places in the European Championship: Caracciola ahead of von Brauchitsch, Lang and the Swiss Christian Kautz. 1937 was both the high point and the end of the 750-kilogram formula, since a new set of rules came into force from 1938.
Along with their successes in formula racing, the racing department in Stuttgart also served up a string of victories in reliability trials and other competitions in the years up to 1938, particularly in touring car events. In 1934, Mercedes-Benz had won four gold medals with the W 150 in the ‘2000 Kilometres Through Germany’ event. In subsequent years the company also competed in many off-road events with a series of vehicles based on the 170 V – the 170 VR, 170 VS, 170 SV, and 200 V.
1938: Victory in the 3-litre formula with the W 154
In September 1936, the motor sport body AIACR laid down the Grand Prix formula specifications that were to apply from 1938. The key points were a maximum displacement of 3 litres for mechanically supercharged engines and 4.5 litres for naturally aspirated engines, and weight from a minimum of 400 kilograms to a maximum of 850 kilograms, according to displacement. These specifications necessitated a completely new car, so the 1937 season was still in full swing when the Mercedes-Benz designers finalised their car for the next racing season.
There was certainly no shortage of ideas in the racing design department: they considered using a W 24 naturally aspirated engine with three banks of eight cylinders each, a rear-positioned engine, direct petrol injection and a fully streamlined body. Mainly for heat reasons, they ultimately opted for a V12 configuration with a V angle of 60 degrees, developed at Daimler-Benz by the old master Albert Heess. The steel cylinders were combined in groups of three in welded-on steel plate cooling jackets, with non-removable heads. Powerful pumps propelled 100 litres of oil per minute through the approx. 250-kilogram engine. Compression was provided initially by two single-stage superchargers, which were replaced in 1939 with a single two-stage unit.
The engine was run on the test bench from January 1938. Then during its first virtually problem-free trial run on 7 February it developed 314 kW at 8000 rpm. The power available to the driver was 316 kW in the first half of the season, climbing to over 344 kW by the end of the racing year. The most powerful version of the engine was the 349 kW unit used by Hermann Lang in Reims, where his W 154 hurtled down the straight sections at a speed of 283 km/h at 7500 rpm. This was also the first Mercedes-Benz racing car to have a five-speed gearbox.
The changes made for the W 125 by chassis designer Max Wagner were much less extensive – the chassis was virtually unchanged from the previous year, although he did take the opportunity to increase the frame’s torsional rigidity by 30 per cent. The V12 engine was deeply recessed, with the carburettor air inlets positioned in the middle of the radiator. The radiator grille became ever wider as the beginning of the season approached. The driver sat on the right, beside the propeller shaft. The W 154 crouched low over the asphalt, with the tops of the wheels well above the contours of the body. As well as enhancing the dynamic look of the car, this substantially lowered the centre of gravity. The racing drivers, as chief designer Rudolf Uhlenhaut’s implicitly trusted consultants, were immediately impressed with the road-holding qualities of the new racer.
The W 154 was indeed able to outdo the exploits of its predecessor: this Silver Arrow gave the Mercedes-Benz racing department its greatest number of victories during this era. The first race of the new season ended in disappointment, as the car was unable to display its full potential on the twisting circuit in Pau, France, and was set back by a refuelling stop. But things rapidly improved thereafter. The Tripoli Grand Prix resulted in a triple victory for Lang, von Brauchitsch and Caracciola, a feat repeated at the French Grand Prix in the sequence von Brauchitsch, Caracciola and Lang. The British driver Richard Seaman, who had joined the team in 1937, won the German Grand Prix at the Nürburgring ahead of the car driven jointly by Caracciola and Lang, while Hermann Lang took the Coppa Ciano in Livorno and Rudolf Caracciola the Coppa Acerbo at Pescara. At the Swiss Grand Prix, the W 154 again filled all three places (Caracciola, Seaman, and von Brauchitsch). Rudolf Caracciola became European champion for the third time. Weakened by the death of its top driver Bernd Rosemeyer during record-breaking attempts in January 1938, Auto Union was unable to post any successes until towards the end of the season.
1938: W 125 becomes the fastest car ever on the open road
Having recognised the prestige value of record-breaking drives, the Supreme National Sports Authority in Germany (ONS) organised an international record week in October 1937 on the Frankfurt–Darmstadt autobahn, although in fact almost all participating vehicles were German. It ended in a clear triumph for Auto Union, with Bernd Rosemeyer establishing a string of new top speeds, including becoming the first driver to go above 400 km/h on a public road. In contrast, the Mercedes-Benz cars were rather disappointing and were recalled prematurely to the factory. But in January 1938, ahead of the Berlin Motor Show, the company management succeeded in arranging for another series of record-breaking attempts to be made on the same stretch of road. This time, in a much improved vehicle, Rudolf Caracciola set another speed record, one which still stands to this day. In a 12-cylinder record car based on the W 125, he achieved the fastest speeds ever recorded on the open road: 432.7 km/h for the flying start kilometre, and 432.4 km/h for the flying start mile. But an attempt by Auto Union star driver Bernd Rosemeyer to recapture this record immediately afterwards ended tragically, when his car, travelling at full speed, was blown off the road by a gust of wind.
Caracciola’s record car, like the other Mercedes-Benz’s other such vehicles from this period, was adapted specifically for the purpose by wind tunnel testing. The only record car to be largely unchanged from the Grand Prix equivalent was the W 25 with which Mercedes-Benz broke the Class C record (3 to 5 litres displacement) in late 1934 at Gyön in Hungary. The sole design change in this case was to place a hood over the open cockpit, which was why Rudolf Caracciola called the car his ‘racing saloon’. The Hungarian record-setting drive was Mercedes-Benz’s response to the one-hour record set by Auto Union in March 1934, and marked the beginning of a speed duel between the two brands over the next few years.
The record car of 1936 was the most spectacular adaptation of the W 25 – built on the same chassis, but with fully streamlined fairings, even including the wheels and the underbody. The car was developed in the wind tunnel at the Zeppelin plant in Friedrichshafen. The body weighed in at around 100 kilograms, and achieved a sensational drag coefficient of cd = 0.235. It was powered by a V12 engine developing 453 kW, displacement 5577 cc, with the code name MD 25 DAB/1. The engine had been intended for Grand Prix competition, but proved to be too heavy. Caracciola notched up many of his Class B triumphs in this car, such as a world flying start ten-mile record of 333.5 km/h. The vehicle’s top speed was 372 km/h.
Another product of wind-tunnel testing, this time at the German Institute for Aviation Research, Berlin-Adlershof, with a cd value of 0.157, was the 1938 record car version of the W 125. Powered by the latest evolution stage of the 5.6-litre 12-cylinder engine, it created a record that still stands today, with the fastest speeds ever recorded on the open road: 432.7 km/h for the flying start kilometre, and a top one-way speed of 436.7 km/h. Two Roots superchargers boosted its power to 541 kW at 5800 rpm. An earlier design stage of the 6.25-metre long vehicle tended to lose adhesion with the road surface at speeds of 400 km/h. Rudolf Uhlenhaut reduced the front surface area to the bare minimum to reduce the flow resistance of the radiator, so that all the air required by the huge V12 engine came from two small ‘nostril’ openings. The optimum operating temperature over short distances was achieved with a normal W 125 radiator, embedded in a box placed on two supports in front of the engine, filled with half a cubic metre of ice and water.
By 1939, design specialisation had increased to the point of creating two contemporaneous record versions of the W 154 for Class D (displacement of 2 to 3 litres): one car designed for maximum flying-start speeds, and another variant with faired wheels and a distinctive notched section in the cockpit area for standing-start sprints. Common features were the similarity of the design to the current Grand Prix monoposto and the choice of driver: these records, too, were set by Rudolf Caracciola.
With ever higher speeds, the demands of these ‘silver bullets’ increasingly began to exceed the capacity of the available tracks. In 1934 all that was needed had been a smooth, straight section of concrete in Gyön, near Budapest, or the Avus track in Berlin, just as it was – but record attempts just two years later required the use of the Frankfurt–Heidelberg autobahn, and eventually an extensive stretch of the new autobahn between Dessau and Bitterfeld.
The last record attempt of this kind on an autobahn took place in February 1939. The 1939 W 154 record car developed 344 kW at 7800 rpm, and featured a futuristic-looking, fully streamlined body for the flying start and individual wheel fairings for the standing start. On this occasion Caracciola set the following international records for Class D (displacement of 2 to 3 litres), in a Mercedes-Benz W 154 record car: 175.1 km/h for one kilometre with a standing start, 204.6 km/h for one mile with a standing start, 398.2 km/h over one kilometre with a flying start, and 399.6 km/h over one mile with a flying start.
The Mercedes-Benz T 80 of 1939, 8.24 metres long and with three axles, was designed to break the world land speed record, which in a duel between the two British drivers George Eyston and John Cobb in August 1939 had been ratcheted up to 595 km/h on the salt flats in Utah, USA. This mighty beast was to be powered by a V12 DB 603 RS aircraft engine, weighing 807 kilograms, with a displacement of 44,500 cc and developing 2,574 kW at 3640 rpm. Because of the outbreak of the Second World War, however, the T 80 was never actually used.
1939: Race victories with 3- and 1.5-litre displacements
In the last racing season before the start of the Second World War, Mercedes-Benz managed to continue the success story from 1938 with the W 154. The first race on the calendar, the Pau Grand Prix, was won by Hermann Lang in a W 154 ahead of Manfred von Brauchitsch, making up for the defeat suffered the previous year. Lang was again the winner in the Eifel event in May, with Caracciola in third place and von Brauchitsch fourth.
Lang went on to extend this impressive winning streak. He took the Höhenstrassen-Rennen (High Road Race) in Vienna in a hillclimb version of the W 154 (with von Brauchitsch in third place), followed by an identical result for the same two drivers in the Belgian Grand Prix at Spa. Caracciola took the German Grand Prix at the Nürburgring – for the fifth time. At the Swiss Grand Prix Lang finished ahead of Caracciola and von Brauchitsch. He also won the German Hillclimb Grand Prix on the Grossglockner, thereby securing the 1939 German Hillclimb title. He was clearly the season’s top driver, but with the outbreak of war the authorities responsible, the AIACR in Paris, were unable to award the title of European Champion. Under the regulations at the time the championship should have gone to Hermann Paul Müller of Auto Union, on the basis of good placings in the four championship races, but the national ONS organisation declared Hermann Lang the champion.
A departure from the norm in the series of Mercedes victories in 1939 was the Tripoli Grand Prix. For this race, the 3-litre specification that had been totally dominated by the German racing cars was replaced by a 1.5-litre category (voiturette formula), for which the Stuttgart engineers had no vehicle. This was a ruse by the organisers in Libya – at that time an Italian colony – designed to circumvent the domination of the Silver Arrow cars and to ensure the first victory for an Italian car in the event since 1934. Since that year the race on the Mellaha track had been won by German drivers: Caracciola in 1935, a victory for Auto Union in 1936, and Hermann Lang for Mercedes in 1937 and 1938.
But Mercedes-Benz was not to be eliminated so easily from what was in the 1930s one of the most prestigious Grand Prix events. When the changes to the rules were announced in September 1938, the team in Stuttgart took just eight months to develop a completely new racing car, the W 165. The basic drawings were soon completed by engine specialist Albert Heess and chassis master Max Wagner, and by April 1939 both Caracciola and Lang were testing the first car in Hockenheim. And so, to the amazement of the racing world, the starting line-up for the Gran Premio di Tripoli included two Mercedes-Benz W 165s with the required 1.5-litre displacement.
The new car was based on the current W 154 Grand Prix car, and at first glance appeared to be a scaled-down version of the 3-litre racer. The struts of the oval frame were made of chromium-nickel-molybdenum steel, with the five cross-members supplemented by the rear engine bracket. The driver sat not in the middle, but slightly to the right. With full fuel tanks but without the driver, the W 165 weighed 905 kilograms. The engine, too, even though it weighed just 195 kilograms, was clearly a close relation of the V12 engine in the W 154. It was a V8 engine with displacement of 1493 cc, a V angle of 90 degrees, and with four overhead camshafts and 32 valves, with an almost identical arrangement and drive system to those in the Grand Prix model. The mixture was prepared by two Solex suction carburettors, with powerful support from two Roots blowers. Its output of 187 kW at 8250 rpm equated to an astonishing power per litre of 125 kW. Large brake drums (diameter 360 mm) covered almost the whole of the inside part of the spoked wheels. The designers had even allowed for the extreme temperatures to be expected in this particular host country – where the track baked in temperatures of 52 degrees Celsius on the day of the race – by placing tubular coolers along the fuel line.
The rest is racing history: the two Mercedes-Benz W 165s left their adversaries virtually no chance. Caracciola, in his shorter-ratio vehicle, completed the entire race without a break, while Hermann Lang – in line with Neubauer’s carefully planned tactics – made a brief stop to change tyres and won the Tripoli event in his taller-ratio car (giving him a higher maximum speed), almost an entire lap clear of his fellow Mercedes driver.
The last start by a Silver Arrow car in 1939 was in the second Belgrade City Race on 3 September. Manfred von Brauchitsch finished second in his W 154 behind Tazio Nuvolari for Auto Union. But by this time the Second World War had already begun.