1932 was hardly a stellar year for motor sport in Germany, with unemployment, the economic depression and the closure of the Mercedes-Benz works racing department. There were, however, good prospects for the future, from the introduction in 1934 of a new formula for grand prix motor racing.
The new rules stipulated a maximum weight of 750 kilograms, without fuel, oil, coolant and tyres, and otherwise no restrictions. 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 sheer weight alone was enough to bar any possibility of adaptation for racing purposes, at double the new maximum figure.
Mercedes-Benz made the decision to develop a new racing car in 1933, following continual pressure for a return to the racetrack from racing manager Alfred Neubauer. However, 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 prompted it to continue existing Autobahn construction projects, lower tax on new cars, and encourage leading automakers to become involved in racing. This was the origin of the rivalry between Mercedes-Benz and Auto Union, which was to dominate the European racing scene in the years up to 1939.
One of the first drivers Neubauer contacted was Rudolf Caracciola. The other team members were Manfred von Brauchitsch, Luigi Fagioli, Hanns Geier and Ernst Henne. By the winter of 1933, Neubauer was delighted with the prospects of an elegant monoposto, designed to carry the white colours of the German national team to victory after victory. So at this stage, the car was still intended to be white. The change from white to silver occurred only during the 1934 season, but for pragmatic rather than design or image reasons.
A team of engineers led by principal design bureau head Hans Nibel were working under intense time pressure on the development of their new monoposto. The front engine may have been rather conservative in comparison with Auto Union’s mid-engine and earlier designs such as the Benz ‘Tropfenwagen’, 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 racetrack. The chassis was the responsibility of Max Wagner, and the engine was the domain of Albert Heess and Otto Schilling. Meanwhile, in the research department under Fritz Nallinger, Georg Scheerer, who had also assisted at the birth of DMG’s Kompressor car, was running exhaustive tests on the engine. Otto Weber assembled the engine, and Jakob Kraus fitted the chassis – both of them veterans 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 highway between Milan and Varese. The 320-hp (235-kW) car (later boosted to 354 hp/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 Mercedes-Benz pulled out because of technical problems. Accordingly, the new car made its first appearance one week later, at the international Eifel race on 3 June. The W 25 lined up at the start in silver – supposedly, as the legend has it, after the cars on the Nürburgring had been stripped of their white paint to bring them under the 750 kilogram limit as required by the new formula rules.
So the Eifelrace in 1934 was the first start for the new Mercedes-Benz formula tracing 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 in the Coppa Acerbo and a Mercedes-Benz victory in the Italian Grand Prix in Monza. A total of 1276 curves and 928 chicanes during the race made Monza the most demanding event on the 1934 racing calendar. Following his accident in Monaco in 1933, Rudolf Caracciola was still not fit enough to make it through the entire race. Because of severe hip pains, halfway through the race Luigi Fagioli took over at the steering wheel of Caracciola’s car, carrying the start number 2. Technical problems with his car had forced Fagioli out at an early stage of the race, but he successfully defended the lead Caracciola had built up on the field by that stage, and was first across the finish line. Fagioli also won the Spanish Grand Prix ahead of Caracciola, and finished second in the Masaryk Grand Prix.
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 record car to an international speed record for class C (displacement of three to five litres) for the flying start one kilometre and one 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 1934, Caracciola then set an international C class record of 311.98 km/h on the Avus track, with his W 25 record car fitted with a streamlined bonnet.
However, 1934 also saw some tough competition from Auto Union as the newcomer on the scene. The Stuttgart company responded in the 1935 season with several new generations of the W 25. The most powerful of the range of engines, the M 25 C, developed 462 hp (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. This made the No. 1 driver of the Silver Arrow team the European champion for 1935.
The same year brought victories for Luigi Fagioli in the Monaco Grand Prix, the Avus race and the Barcelona Grand Prix (with Caracciola in second place). The 1936 version of the W 25, developing 449 hp (330 kW), with a shorter wheelbase, was not able to replicate the string of successes achieved in 1935. The new season brought only two grand prix victories for Mercedes-Benz, in Monaco and Tunis (both Caracciola). 1936 proved instead to be the year of Auto Union and Bernd Rosemeyer.
1937: the year of the W 125
Following the less than outstanding performance of the modified W 25 in its third season, Mercedes-Benz developed a new car for the 1937 racing year, the last year under the current formula rules. As a foretaste of the innovations in store from the racing department in Stuttgart, on a single day – 11 November – Rudolf Caracciola broke five international records and one world record on the autobahn between Frankfurt and Darmstadt, in a Mercedes-Benz 12-cylinder record car.
The 1937 racing year was dominated by the eight-cylinder W 125 monoposto. The engine again included a mechanical supercharger, developing over 600 hp (441 kW) from a displacement of 5.6 litres. The W 125, designed by Rudolf Uhlenhaut, put Mercedes-Benz back at the top of the European motor racing scene. The design included numerous innovations in matters of detail. For the first time in a Silver Arrow car, the supercharger was placed after 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 used since the 1934 season.
The backbone of the car was an ultra-robust frame of special steel, with four crossbars. There were also modifications in the wheel design. 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-jointed drive shaft providing constant camber adjustment, with longitudinal torsion bar springs and hydraulic lever-type shock absorbers. Shear and braking torque was transferred to the chassis by lateral links.
After extensive test drives on the Nürburgring racetrack, Uhlenhaut opted for a revolutionary chassis design in terms of the chassis adjustment. He made a bold and visionary decision to replace the customary principle of hard springs and minimum shock absorption with the precise opposite. The W 125 featured soft sprung suspension and exceptionally long spring travel, with a high level of shock absorption, 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 in the front section. The car generally 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 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. In the Eifel race, Caracciola and von Brauchitsch finished in second and third places, respectively, 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 ‘Freddie’ 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. He also won the Masaryk Grand Prix, with von Brauchitsch in second place. This gave Caracciola another European championship title, at the end of a record year for Mercedes-Benz.
Mercedes-Benz’s outstanding success with the W 125 in 1937 could never be replicated, since this was the last season of the 750-kilogram formula. The new rules introduced the following year restricted displacement to three litres with a mechanical supercharger, or 4.5 litres without. The creators of the Silver Arrow yet again set about meeting the challenge in the development department and on the track, developing an entirely new racing car for 1938 to pick up where their 750-kg champions had left off.
Along with their successes in formula racing, the racing department in Stuttgart also delivered 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 in the ‘2000 kilometres through Germany’ event, with the W 150. 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 three-litre formula with the W 154
In September 1936, the motor sport body AIACR (Association Internationale des Automobile Clubs Reconnus) laid down the grand prix formula specifications to apply from 1938. The key points were a maximum displacement of three litres for mechanically supercharged engines and 4.5 litres for aspirating engines, and minimum weight of 400 to 850 kilograms, on a sliding scale according to engine capacity. These specifications necessitated a completely new car, but 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 even considered using a W24 aspirating engine with three banks of eight cylinders each, placed at the rear, 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 by the old master Albert Heess himself at Daimler-Benz. 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 250-kilogram engine. Compression was provided initially by two single-stage superchargers, which were replaced in 1939 with a single two-stage device.
The engine was run on the test bench from January 1938. On its first almost problem-free trial run on 7 February, it developed 427 hp (314 kW) at 8000 rpm. The power available to the drivers was 430 hp (316 kW) in the first half of the season, climbing to over 468 hp (344 kW) by the end of the racing year. The most powerful version of the engine was the 474-hp (349-kW) unit used by Hermann Lang in Reims, where his W 154 hurtled down the numerous 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 percent. The V12 engine was deeply recessed, with the carburettor air inlets in the middle of the radiator. The radiator grille became ever wider as the beginning of the season approached. The driver sat at the right, beside the drive 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. Manfred von Brauchitsch and Richard Seaman, 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. Its very first race, 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 won the German Grand Prix at the Nürburgring ahead of the car driven by Caracciola and Lang, while Hermann Lang took out 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.
1938: W 125 becomes the fastest car ever on the open road
During the highly successful 1938 racing season, Rudolf Caracciola set yet another speed record, which still stands to this day. In a Mercedes-Benz 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. An immediate attempt by Auto Union star driver Bernd Rosemeyer to break this record ended tragically, when his car, travelling at full speed, was blown off the road by a wind gust.
Caracciola’s record-breaking 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 (three to five litres displacement) in late 1934 at Gyön in Hungary. The only design change in this case was to place a hood over the open cockpit, which was why Rudolf Caracciola called the car his ‘racing sedan’. The Hungarian record-setting drive in 1934 was Mercedes-Benz’s response to the one-hour record set by Auto Union, and marked the beginning of a speed duel between the two brands over the next few years.
The record-setting car of 1936 was the most spectacular adaptation of the W 25 – 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, weighed in at around 100 kilograms, and achieved a sensational drag coefficient of cd=0.235. It was driven by a V12 engine developing 616 hp (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 ten-mile flying start record of 333.5 km/h. The vehicle’s maximum 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-setting 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 one kilometre, and a maximum one-way speed of 436.7 km/h. Two Roots superchargers boosted its power to 736 hp
(541 kW) at 5800 rpm. An earlier design stage of the 6.25-metre long vehicle tended to lose contact with the road surface on reaching 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 two to three litres): one car designed for maximum highest flying-start speeds, and another variant with faired wheels and a distinctive notched section in the cockpit area for standing sprints. Constant features were the similarity of the design to the current grand prix monoposto, and the choice of driver: these records, too, were set by top racing driver Rudolf Caracciola.
With ever higher speeds, the demands of these ‘silver bullets’ increasingly began to exceed the capacity of the available tracks. All that was needed in 1934 was 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 468 hp (344 kW) at 7800 rpm, with 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 two to three litres), in a Mercedes-Benz W 154 record car: 175.1 km/h for the standing start kilometre, 204.6 km/h for the standing start mile, 398.2 km/h for the flying start kilometre, and 399.6 km/h for the flying start mile.
The Mercedes-Benz T 80 of 1939, 8.24 metres long and with three axles, was designed to break Malcolm Campbell’s world speed record of over 484 km/h. This mighty beast was to be driven by a V12 DB 603 RS aircraft engine, weighing 807 kilograms, with a displacement of 44,500 cc, developing 3500 hp (2574 kW) at 3640 rpm. Because of the outbreak of the Second World War, however, the T 80 was never actually used.
1939: racing victories in the three-litre and 1.5-litre displacement categories
In the last racing season before the start of World War II, Mercedes-Benz managed to continue the success story from 1938 with the W 154. The first race on the calendar was the Pau Grand Prix, won by Hermann Lang in a W 154, ahead of Manfred von Brauchitsch. Lang was again the winner in the Eifel event in May, with Caracciola in third place and von Brauchitsch fourth. Lang maintained this consistent performance throughout the season, ending the year as the European champion and German mountain champion.
Lang won the Höhenstrassen race in Vienna in a mountain 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 in Spa. In the Swiss Grand Prix, Lang was the first across the line, ahead of Caracciola and von Brauchitsch. Caracciola won the 1939 German Grand Prix at the Nürburgring, and was German touring car champion for the year.
A departure from the norm in the series of Mercedes victories in 1939 was the Tripoli Grand Prix. For this race, the three-litre specification where Mercedes-Benz had carried all before it was replaced by a 1.5-litre category (voiturette formula), for which the Stuttgart engineers had no vehicle available. This was a trick 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 then, the race on the Mellaha track had been won by German drivers: Caracciola in 1935, 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 one of the most popular grand prix events in the 1930s. Following the change of rules published in September 1938, the team in Stuttgart took just eight months to develop a completely new racing car, the W 165. The key drawings were completed by engine specialist Albert Heess and chassis master Max Wagner by mid-February 1939, and by April both Caracciola and Lang were testing the first car in Hockenheim. So it was that, to the amazement of the racing world, the starting line-up for the Tripoli Grand Prix 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 miniature version of the three-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 somewhat to the right-hand side. 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 unit 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, arranged almost identically to those in the grand prix model. The mixture was prepared by two Solex suction carburettors, with powerful support from two Roots blowers. Its rating of 254 hp (187 kW) at 8250 rpm equated to a power per litre of an amazing 170 hp (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 was baking at a temperature 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 wheelbase vehicle, completed the entire race on one set of tyres, while Hermann Lang – in line with Neubauer’s carefully planned tactics – made a brief stop and won the Tripoli event in his longer wheelbase vehicle (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 30 September. Manfred von Brauchitsch finished second in his W 154, with a maximum speed of 121.9 km/h. But by now World War II had already begun.
Source: Daimler AG