Silver Speedsters

Mercedes-Benz Speed-Record Cars, 1934-1939

Article Graham Robson

Images Daimler Archives

How on earth did they manage it – and how could they find the time? These days, maintaining just two state-of-the-art Mercedes-Benz racecars on the F1 circuits of the world requires more than a thousand highly dedicated team members at Mercedes AMG Petronas facilities at Brackley and Brixworth in England. Compare this with preparing a much larger stable of Grand Prix cars for racing between 1934 and 1939 – a task likely accomplished with fewer than 50 people.

That was a miracle in itself. And while it’s true there were not as many major events to tackle in those days, somehow there also was time during the winter for crew members to turn their attention to building a series of ultra-fast machines to pit against both existing speed records and the cars of the company’s great rival of the day, Auto Union. How on earth did they do it? We have no idea, but it was done with great flair and success.

Early W25 speed-record cars

The first of the legendary Mercedes-Benz Silver Arrow Grand Prix cars arrived in 1934; in addition, the company was already thinking of experimenting with cars that would challenge land-speed records during the winter months when there were no Grand Prix events scheduled to keep technicians occupied.

This first project was based on a rather quaint-looking W25 car, with chassis and running gear closely related to that of the then-current GP machines. There were two versions – both with fully exposed wheels and much smaller frontal air intakes – but one of them had a smart if claustrophobic bubble hardtop; the other employed an open cockpit.

Whereas the 8-cylinder engine of the W25 GP car produced 348 brake horsepower, that of the record car, enlarged to 4.0-liters, and boosted by the use of exotic fuel and higher supercharger pressure, produced a remarkable 430 brake horsepower.

The cars began speed trials on a new concrete highway at Gyon, Hungary, near Budapest, in October 1934. The open-top car was at once crippled with a broken engine. However, Rudolf Caracciola (see The Star, July-August 2016) steered the coupe to no less than 196.78 mph. This was far higher than had ever before been achieved by a 3.0- to 5.0-liter machine.

In December, Caracciola drove the same closed car on the new “Automobil-Verkehrs-und Übungsstrasse” or AVUS (Automobile Traffic and Practice Road), a hybrid test track and controlled-access highway built near Berlin. AVUS was a designated stretch of autobahn modified to include a steeply banked hairpin bend which allowed the segment to be shut off for use as a high-speed closed circuit.

Caracciola’s attempt that day yielded no new record. The closed-top design was then retired once and for all: Although in the future, air would be rushing past an open cockpit at over 250 mph, at least the driver could cling to the hope that if a rapid exit from the vehicle did became necessary, doing so would be far easier!

Although Mercedes-Benz made no further top-speed attempts in 1935, the firm returned with a vengeance in 1936. Even though the latest GP car, the W25, was not a racing success – mainly due to indifferent handling – its chassis was used for speed-record purposes, complete with elegantly streamlined coachwork and a brand-new V-12 engine.

The new DAB engine had a 60-degree V-angle, twin camshafts on each cylinder bank and two valves per cylinder, and measured 5,577cc. It was originally intended for use in the GP machines, but weighing 250 pounds more than the existing 8-cylinder GP engine, proved too large and heavy for circuit racing. The engine’s power output was never a problem – tests showed that it developed 570 brake horsepower. For speed record attempts, that would be boosted to 616 brake horsepower. Once it was installed in the new machine, the point was proved.

The 1936 record breaker was perhaps the prettiest of the entire breed, not only shattering a host of records on new German autobahns over two years, but also looked so neat, and was clearly a wind-cheater as well. High-speed air-flow testing was carried out in the wind tunnel at the Zeppelin airship works at Friedrichshafen on Lake Constance in the south of Germany – an early instance of an aeronautical wind tunnel employed to test automobile aerodynamics.

The silver car’s initial speed-record attempts began in October-November 1936. Mercedes-Benz selected a section of the brand-new Frankfurt-Darmstadt Autobahn near Frankfurt Airport where, with Caracciola at the wheel, the car reached a stunning 228 mph. But this was only a start. At a Formula Libre (Free Formula) race at AVUS in spring 1937, the streamliner was assigned to Manfred von Brauchitsch. The car ran without road-wheel covers to assist brake cooling when slowing the vehicle for the tight turns at the ends of the circuit.

Perhaps it was unrealistic to expect such a specialized vehicle to win a longer-distance race, particularly as there was very strong competition from Auto Union, but von Brauchitsch did his best, winning the second of three heats; ultimately, the car’s transmission failed in the final heat.

W125 speed-record car

No matter, for in 1937 the team came up with yet another version, this time a W125-based record car, now fitted with a colossally powerful 736-horsepower version of the DAB V-12 engine, and with a heavily revised version of the same streamlined bodywork – 8.7 inches narrower and up to 4.7 inches lower than the previous speed-record car: The new vehicle’s drag coefficient had been reduced to an incredibly low 0.181.

Once again, the chosen driver was Caracciola; once again, the venue was the new Frankfurt-Darmstadt Autobahn. This time the Mercedes-Benz ace reached 248 mph. Sadly for company publicists, a sleek Auto Union streamliner also competing reached an amazing 252 mph.

Deeply stung – and equally determined to have good news to trumpet before the Berlin Motor Show in February – the Mercedes-Benz team toiled around the clock to improve their latest machine. Although the only obvious outward change was a smaller, two-piece front air intake, water and ice were added to the car’s enlarged cooling system and extensive refinement in the wind tunnel reduced the drag coefficient to 0.157.

During winter 1937-1938, in the middle of Germany’s preparations for war, there was little time for testing – and none at all for leisurely practice and experimentation – so it was remarkable that the car turned up at the then-familiar Frankfurt-Darmstadt site, and that the first and only record runs were made early in the morning of January 28, 1938.

Caracciola, as smooth and unruffled as ever, had settled into his car with a smile, pointed it up the none-too-wide autobahn and recorded a colossal 268.49 mph. According to his published quote afterward: “The car hugged the road beautifully. …” To this day, no other car has achieved a higher speed on what was essentially a public road. By 9 a.m. that day, new records had been established; the team then loaded up car and equipment and returned home to Stuttgart.

Even so, the W125-based machine might have done even better on a new road between Dessau and Bitterfeld, between the cities of Hanover and Dresden. This part of the new autobahn – which ran north-south – was specifically built for high-speed testing, for on one designated five-mile segment, the central median had been concreted over, creating an autobahn that was no less than 100 feet wide on that stretch. The team decamped there in February 1939, but did not run because of unsuitable conditions.

W154 speed record car

Appearing in 1939, the last of the conventional prewar speed-record cars was totally new and visually very different from its predecessors. This advanced vehicle was based on the chassis and running gear of the 1938-1939 W154 GP cars, which used a 60-degree V-12 M154/M163 3-liter engine (Grand Prix regulations having changed at the start of the 1938 season). In normal, open-wheel road racing form, this machine produced approximately 450-460 horsepower; output was boosted to 468 horsepower for the record-attempt car in 1939.

While the chassis and running gear were well known by 1939, the shape of the new record car was quite novel and, in its own way, astonishing. Every lesson offered by the experience of the W25/W125 types, with their extremely powerful engines, had been learned. The team was anxious to squeeze every possible element of speed out of this 3-liter-engine machine, which would be attacking different capacity class records.

Strangely enough, not only did this car look different from its predecessors, but it was also quite a bit less aerodynamically “clean” than before. It was by no means as integrated in style; some observers likened it to a road-racing W154 in which the main elements of the racecar’s body shell had been retained, mated to four distinct nacelles covering the road wheels. According to published figures, the Grand Prix open-wheeler had a drag coefficient of 0.599, while the record car’s equivalent figure, with wheel covers fitted and all, was down to Cd 0.293.

The only major attempt to reduce drag was to limit the front air intake to a tiny circular opening. An ice engine-cooling pack was installed in the smooth tail.

The finished car was ready to run at Dessau in February 1939 in what would be its only public appearance. After setting several new standing-start records, Caracciola clocked a momentous 248.3 mph for the flying mile. This was the last time that a Mercedes-Benz record car would appear in public until the 1970s.

It is intriguing to recall that the original 1934 speed-record contender had reached a speed of 196.78 mph with a 430-horsepower engine, and that less than five years later, a 3-liter-engined car producing 468 horsepower reached 248 mph. In that time, it seems so much had been learned about aerodynamics that Mercedes-Benz had pushed up the cars’ top speed by 52 mph while having just 38 horsepower more available with which to do it – a remarkable tribute to the way that the streamlining qualities of the body shells had improved.

The unfinished Type 80

Although the Type 80 never ran – and though the car survives, it will never run under its own power – it was very nearly completed and ready to go in 1939-1940. Only the outbreak of war put a halt to this stupendously ambitious land-speed-record project.

Developed in total secrecy from 1936, its very existence was not known until 1945, when occupying forces inspecting the battered remains of the Mercedes-Benz factory discovered the incomplete machine.

It was Hans Stuck, not himself a regular Mercedes-Benz driver, who in 1936 conceived the idea of a Mercedes-Benz land-speed-record contender. The previous year, Britain’s Sir Malcolm Campbell had recorded 301 mph in his Rolls-Royce aero-engine-powered “Bluebird” on Utah’s Bonneville Salt Flats. Stuck yearned to beat that mark, not only for himself, but also for the greater glory of a new Germany.

His plan, which lacked only money – a great deal of money indeed – was for an advanced new machine to be designed by Dr. Ferdinand Porsche. The vehicle would have a mid-rear engine and six wheels – four in tandem at the rear to handle and tame all the necessary horsepower. It was to be powered by a massive cutting-edge Mercedes-Benz aero engine, the incredible DB601, which was a supercharged V-12 monster slated to become standard in military machines such as the Messerschmitt Bf 109 fighter.

Porsche was fascinated by the idea, but concluded that the challenge – perhaps technically insuperable at the time – was that Stuck’s proposed machine would need to generate somewhere between 2,000 and 2,500 horsepower in order to reach a targeted top speed of around 350 mph. Not even the latest DB601 engine could produce that. Undaunted, Stuck got Mercedes-Benz to agree to build the vehicle and provide the latest engine. Construction began in secrecy in 1937.

Work was hampered by slow development of the engine, but when the new, much larger 44.5-liter DB603 version was run, the secret vehicle began to look competitive – especially considering the futuristic body style was so aerodynamically smooth. Once this more powerful engine was available, Porsche raised his forecast to a top speed of 373 mph.

As the radical new machine neared completion in 1939, the international political situation continued to worsen. The factory team had to abandon earlier plans to use the Bonneville Salt Flats and instead aimed to use the new Dessau concrete road, already sampled by the speed-record team. With 3,000 horsepower expected from the latest engine, all looked promising. However, the outbreak of war in September 1939 killed off all hopes; the promised engine was reallocated to the military. The untested Type 80 was returned to Stuttgart. Stored throughout the conflict, it miraculously survived heavy Allied aerial bombing.

On the Frankfurt-Darmstadt Autobahn October 11, 1936, Rudolf Caracciola established five international category records and a world record with the Mercedes-Benz W25 12-cylinder streamlined car.

Initial Mercedes-Benz W25 speed trials on the new concrete road at Gyon near Budapest, October 28 & 30, 1934.

AVUS circuit, Berlin, December 10, 1934:

Before his run in the bubble-topped W25 coupe, driver Rudolf Caracciola speaks with head engineer Alfred Neubauer (in dark hat).

The W25 reached 193.86 mph. Near Frankfurt, on October 26, 1936, Caracciola set three international class records in the pretty W25 12-cylinder streamliner; on his fourth run, wind resistance dented the little silver car’s nose.

Manfred von Brauchitsch in the W25 12-cylinder streamlined car during practice at AVUS, May 30, 1937.

In the race, the car ran without wheel covers to aid brake cooling.

Titan under the hood: the mighty 736bhp 12-cylinder DAB engine.

On January 28, 1938, Rudolf Caracciola flashes past an unfinished Frankfurt Airport on the Frankfurt-Darmstadt Autobahn in the futuristic 12-cylinder W125 during his historic run to 268.49 mph. Ninety minutes later, his great rival, the dashing Auto Union driver Bernd Rosemeyer, was killed while trying to break the new record on the same stretch of autobahn.

MAIN IMAGE: February 9, 1939 on the Dessau-Bitterfeld Autobahn, Rudolf Caracciola reaches 248.3 mph for the flying mile in the Mercedes-Benz 12-cylinder W154.

ABOVE: The radical Type 80 Streamliner of 1939-1940, seen in period. The car, which never ran, is preserved at the Mercedes-Benz Museum in Stuttgart.

Mercedes-Benz Speed-Record Cars 1934-1939

Year    Model                       Engine                   Speed            Location
1934    W25 coupe              3,980cc/430bhp    196.78 mph    Gyon, Hungary
1934    W25 coupe              3,980cc/430bhp    193.86 mph    AVUS, Germany
1936    W25 streamliner      5,577cc/616bhp     228.0 mph      Frankfurt, Germany
1937    W125 streamliner    5,577cc/679bhp     248 mph         Frankfurt, Germany
1938    W125 streamliner    5,577cc/736bhp     268.49 mph    Frankfurt, Germany
1939    W154 streamliner    2,963cc/468bhp     248.3 mph      Dessau, Germany
Unfinished
1939    Type 80 streamliner 44,500cc/3,000bhp    373mph      Dessau, German

SIDEBARS

Mercedes-Benz & Auto Union

Early in 1934, upstart Auto Union set a new one-hour world speed record, at once demonstrating its technical prowess and throwing down the gauntlet to Mercedes-Benz. From 1934 to 1939 – driven by pride and skill to outdo each other – the pair of  manufacturers vied for victory on Europe’s racetracks, fame in the international speed ledger, and the attention of the German public. In early 1938, after Auto Union driver Bernd Rosemeyer died while trying to break a new record set by Rudolf Caracciola, some of the heat began to go out of the rivalry.

TOP TO BOTTOM: Initial Mercedes-Benz W25 speed trials on the new concrete road at Gyon near Budapest, October 28 & 30, 1934. AVUS circuit, Berlin, December 10, 1934: Before his run in the bubble-topped W25 coupe, driver Rudolf Caracciola speaks with head engineer Alfred Neubauer (in dark hat). The W25 reached 193.86 mph. Near Frankfurt, on October 26, 1936, Caracciola set three international class records in the pretty W25 12-cylinder streamliner; on his fourth run, wind resistance dented the little silver car’s nose.

FROM THE TOP: Manfred von Brauchitsch in the W25 12-cylinder streamlined car during practice at AVUS, May 30, 1937. In the race, the car ran without wheel covers to aid brake cooling. Titan under the hood: the mighty 736bhp 12-cylinder DAB engine. MAIN IMAGE: On January 28, 1938, Rudolf Caracciola flashes past an unfinished Frankfurt Airport on the Frankfurt-Darmstadt Autobahn in the futuristic 12-cylinder W125 during his historic run to 268.49 mph. Ninety minutes later, his great rival, the dashing Auto Union driver Bernd Rosemeyer, was killed while trying to break the new record on the same stretch of autobahn.