Concepts · 1937–1940
The fastest car that never moved.
Six wheels, forty-four and a half liters of aero engine and a calculated 650 km/h. Mercedes-Benz stopped work in February 1940 and put it away.
The T 80 ran for the first time on 12 October 1939, and it did not go anywhere. In a test house at Untertürkheim its wheels turned against a rolling road while the car itself stood perfectly still — which is, in the end, the whole story.
It was eight and a quarter meters long, ran three axles and six wheels, and carried a 44.5-liter Daimler-Benz aero engine behind the driver's back. Ferdinand Porsche's office had calculated 650 km/h for it. Four months after that first run, with nowhere left in Europe to drive it and an air ministry that wanted its engine back, Mercedes-Benz stopped work. Everything you have read about it doing 750 km/h came afterwards, from people guessing.
Chapter I
A driver who needed a record
By the mid-1930s Daimler-Benz and Auto Union were fighting a private war on closed sections of autobahn, and the record books filled with class and world records — staged, in 1937, as an entire Record Week. The one record nobody in Germany touched was the big one. The absolute land speed record already stood near 485 km/h in 1935, a speed no public road could offer with any margin of safety. It belonged to men like Malcolm Campbell, George Eyston and John Cobb, who built their own aero-engined machines and took them to the Bonneville Salt Flats in Utah.
Hans Stuck watched with particular interest. Auto Union's number one was being eclipsed by the young brilliance of Bernd Rosemeyer, and he went looking for a stage of his own: he would use his excellent connections in the National Socialist elite to have Daimler-Benz and Ferdinand Porsche's design office build him an aero-engined car, and bring the absolute record to Germany.
What made him credible was that he arrived with an engine. Stuck secured access to a Daimler-Benz DB 601 — an extraordinary thing to obtain, because every aero engine built in Germany was under the exclusive control of the Luftwaffe's Technical Office. Its head, Ernst Udet, had been a personal contact of his for years.
Wilhelm Kissel of the Daimler-Benz board, who never tired of demonstrating that his company led in both cars and aero engines, was won over; so was Porsche, who was short of contracts. On 13 January 1937 Porsche's office was commissioned to build it.
Chapter II
Porsche's arithmetic
The first target was 550 km/h. Then more news arrived from America, and it became 600, and finally 650 km/h. Porsche's office calculated what that would need: about 3,500 PS.
His answer was not to add engines but to take everything else away. The British cars used two engines and had more than 1,000 PS in hand; the T 80 would run one engine on three axles, far slimmer and far lighter — 2,800 kg dry, less than half the weight of the machines it was chasing. It had no gearbox, because no gearbox existed that would have survived the engine. The crankshaft ran straight into a six-plate heat-storage clutch that adjusted itself by centrifugal force.
One detail in the driveline is startling for 1939. A torque equaliser used a differential and a centrifugal governor to sense the driven rear wheels starting to slip, and cut engine torque until they stopped. Traction control, fitted to save the tires.
Everything else followed the airflow. The three axles ran three different track widths — 1,300 mm at the front, then 1,320 and 1,180 mm behind — narrowing as the body narrowed. The driver sat far forward beneath a fully enclosed canopy cut as narrow as an aircraft's. At 8,240 mm it was the longest racing or record car Mercedes-Benz had ever built.
- Length
- 8,240 mm
- Weight
- 2,800 kg
- Drag coefficient
- 0.18
- Drivetrain
- 6×4
The road
Dessau
South of Dessau, on the Reichsautobahn between Berlin and Halle, ran a straight about ten kilometers long and twenty-five meters wide, its central reservation paved over. Records had been set there in February 1939. It was where the T 80 was meant to go.
Chapter III
Forty-four and a half liters
The DB 601 that had opened the door was a supercharged V12 of about 34 liters, giving 1,100 PS in standard form, with direct petrol injection, four valves per cylinder and twin ignition. Specified for aircraft speed records in 1937 as the DB 601 Re V — higher compression, sharper cam timing, reworked supercharging and volatile fuel — the same engine gave up to 2,770 PS.
Since the autumn of 1936 Daimler-Benz had been building something larger on the same principles. The DB 603 displaced a little over 44.5 liters and was meant for big, heavy military aircraft. Then in March 1937 Ernst Udet stopped its development, because the bomber it had been drawn for could not dive.
That ban is why the T 80's engine was a test unit bought back from the Air Ministry, used for bench running and a provisional installation in the chassis. What it did on the bench was promising: with no special tuning, on racing fuel, 2,800 PS. The 3,500 PS the car needed looked within reach — provided the ministry allowed the same measures already used on the DB 601 Re V. It never did.
Like an aircraft engine it sat inverted, cylinder heads down, which kept the frontal area small. Bore 162 mm, stroke 180 mm, twelve cylinders at sixty degrees, two plugs each, a Bosch pump able to inject 1,500 liters an hour. For the record run it would have drunk a blend called WW: 86 per cent methyl alcohol, the rest acetone, nitrobenzene and ether.
What the arithmetic said
Daimler-Benz figures for the DB 603 in the T 80.
Measured on the test bench, half XM and half WW fuel
2,800 PS· 2,500/min
—
Calculated maximum, half XM and half WW fuel
3,000 PS· 3,200/min
600 km/h
Calculated maximum on WW fuel alone
3,500 PS· 3,460/min
650 km/h
Chapter IV
Nine hundred kilograms of downforce
Every other Mercedes-Benz record car of the 1930s was a Grand Prix car wearing new bodywork. The T 80 was drawn from nothing, and the drag coefficient it reached — 0.18 — is the figure that still stops people.
The skin weighed 132.5 kilograms, beaten by hand, carried on a tubular frame of 124.5 kilograms. Eight quick-release catches held the whole body to the chassis, and it lifted off to change a tire. The body was 1,740 mm wide and 1,270 mm tall — 3,200 mm across, once the wings were on.
Those stub wings were mounted to the frame rather than the body. They are aircraft wings with the profile turned upside down: instead of lift they made downforce, and about 900 kilograms of it was reckoned right to keep the driven wheels pressed into the concrete. Suspension travel was 45 mm up and 42 mm down, small enough that the wheels would not change camber.
Continental made treadless special tires, 7.00-32, 1,170 mm across at rest and calculated to grow to 1,240 mm at 650 km/h. On the rolling road the tires were untroubled. The spoked rims were not: somewhere near 500 km/h they began to deform, and Continental and the rim maker Hering AG started arguing about whose problem that was.
Chapter V
Nowhere left to run
Into the first weeks of 1940 Daimler-Benz still believed the run could happen. The car stood on its six wheels with almost every component and the bodywork close to finished.
Two things stopped it. The Air Ministry's ban on developing the DB 603 held almost to the end, so beyond a few bench runs and that provisional installation there was never a chance to take the engine to 3,500 PS. And after September 1939 there was nowhere to go. Closed autobahn sections were no longer suitable for 650 km/h — the Dessau straight was considered, then set aside — and Bonneville, in the circumstances, was not an option.
All work stopped in February 1940. That same month the ministry was finally persuaded that the DB 603 had a future after all, lifted its own ban — and asked for the engine back. The racing department lifted it out of the car and returned it.
Calculated, never attempted
650 km/h
The speed the T 80 was built for. It was never driven under its own power.
… will not leave its stand in the Daimler-Benz Museum in Stuttgart-Untertürkheim in future either.
Three years and one rolling road
The T 80 was commissioned, built, tested standing still and abandoned inside three years. It took another seventy-eight before its chassis was seen in public.
13.01.1937
Ferdinand Porsche's design office is commissioned to build the record car, as Type 80.
15.03.1937
Ernst Udet halts development of the DB 603 — the aero engine the whole car is designed around.
01.02.1939
The date on the drawing of the finished body: 8,240 mm long, 1,270 mm tall.
12.10.1939
The T 80 runs for the first time, on a rolling road at Untertürkheim.
02.1940
All work stops. The Air Ministry lifts its ban the same month and reclaims the engine.
07.2018
The chassis, with a sectioned DB 603 and a rebuilt tube frame, is presented at the Goodwood Festival of Speed.
Epilogue
A reputation it never earned
The secret did not keep. In November 1945, fresh from a visit to Untertürkheim, the British journalist Laurence Pomeroy published a piece in The Motor under the title “A 450 m.p.h. Car”. A far more detailed account followed in 1948, drawn from the four weeks the British intelligence officer Cameron Earl spent among the Mercedes-Benz and Auto Union racing cars in 1947.
Both put the T 80's top speed at 450 and 464 mph — 724 and 746 km/h. Mercedes-Benz's own view now is that those figures were far too high, given by interviewees who were being generous. That is where the legend of 750 km/h comes from. The company's own arithmetic said 650, and in September 1947 John Cobb went 634 km/h at Bonneville in a car that actually ran.
When the museum was rebuilt in 1986 the T 80 was hung on a wall, which meant cutting the body and its tube frame away from the chassis and drivetrain; the chassis disappeared into the Heilige Hallen, the collection's back rooms. It came out again in 2017 on newly made tires, with a sectioned DB 603 and a rebuilt tube frame, and appeared at Goodwood in July 2018. The body is still in Stuttgart. Mercedes-Benz's position on whether the car will ever run is that it can be ruled out.
One number has aged into something remarkable. In 1939 Porsche's people shaped an eight-meter car to a drag coefficient of 0.18. Eighty-three years later Mercedes-Benz built the Vision EQXX around the same obsession and reached 0.17.