Art of the state: The incredible Auto Union D-Type grand prix car

Auto Union was using two blowers by 1939. Mercedes-Benz had beaten it to this punch in ’38, although those items were in parallel, one per bank on its V12. Both teams were running them in series the following year, a low-pressure unit accepting the charge before squeezing it into its smaller Siamese twin. Auto Union achieved 24psi of boost in this way, an increase of seven from its singleton set-up, and this hiked power from 460bhp to 485 — five up on Mercedes! — at 7000rpm. (Another surprise is that the D-Type ran 10:1 compression, whereas Merc stuck with a conservative 6.5:1.) Of course, drop either V12 into a car weighing the mandatory 850kg minimum minus driver, fluids and tyres and you have a performance that far outstrips, all modern thinking tells you, the road circuits upon which these beasts were unleashed.

This car’s vertical superchargers currently draw from two twin-choke Solex carburettors. However, it is understood that a four-throat, float-less (?), weir-type item was developed for 1939. Entitled the ‘waterfall’, this allowed a jet to draw off exactly what it needed from a chamber topped off by one pump and tapped off at a precise level by another, with any ‘waste’ being recirculated to the main tank. This arrangement also boasted a ram pipe, seen here, that ran underneath the right-hand side of the engine cover before swinging up into and through it.

A colossal backfire — like hitting the brakes — shows that the car is still chilly and grumpy, the methanol freezing around its supercharger inlets. I downshift into first in an effort to keep things ‘on the boil’. The lever is lightly spring-loaded towards the central plane — second, third, fourth and fifth form the usual H-pattern — and its movement is steady rather than rapid. But it exudes quality and solidity, despite a rod linkage that stretches more than 4ft from your right hand to a surprisingly compact, twin-shaft, five-speed gearbox. A dose of double-declutching sees bottom slide into mesh without much of a graunch.

It’s impossible to heel-and-toe, though, which makes things tricky down at the hairpin. But the Lockheed brakes are reassuring. This was another area in which A-U held a slim advantage over cash-rich Mercedes; by 1939, its slotted-backplate, radial-finned, 17-inch drums featured four leading shoes compared to the two of Mercedes. These are operated by a dual-circuit arrangement, the placement of its parallel master cylinders the cause of the wide spacing between throttle and brake. Cold, they grab and pull slightly to the right, locking the fronts once, but they have plenty of feel.

Not that late-1930s GP racing was about stamping on the anchors and banging down the ‘box. Don’t imagine for a minute that Tazio Nuvolari was the first man on the brakes, but the keys needed to unlock those ultra-fast circuits were high-speed balance and terminal velocity. (This was a time, remember, when the hairpin at Eau Rouge was by-passed because Spa’s organisers were worried that their track was too slow!)

Now bear in mind that the Auto Union C-Type was a snap oversteerer, a wild streak tamed only by Bernd Rosemeyer, a tyro blessed with razor-sharp reactions and unencumbered with knowledge of front-engined racing cars. Lesser mortals struggled, while those others with perhaps the talent to adapt preferred to stick with what they knew — and the larger pay packets — at Mercedes. There can be no doubt that an Auto Union weakness during this titanic struggle was its driver line-up; only in 1935 — with Hans Stuck still on it, Achille Varzi getting to grips with it and Rosemeyer coming through — was the east German team able to match the Three-Pointed Star’s stellar squad. Yes, it almost swept the board the following year, but it relied exclusively upon Rosemeyer — and a major backwards step by Mercedes, the unloved W25C — to do so.

So Rosemeyer’s death while record-breaking on the autobahn in January 1938 was an incalculable loss to Auto Union, especially as Dr Ferdinand Porsche, the free thinker behind its mid-engined concept, had just left to concentrate on his VW and build a racing car for Mercedes! Auto Union was a merger of Horch, Wanderer, DKW and Audi; its opinion, understandably, was divided. And the debate was even more fundamental than engine position; shutting up shop was on the agenda. But Prof Robert Eberan von Eberhorst, Porsche’s right-hand man since 1933, was convinced of two things: mid-engined was the way to go, and the company must race on; he got his way on both counts. He was not blind, however, to the problem inherent in Porsche’s design — the new car had to be more driveable — or the need to be clever with the budget. Hitler’s annual 450,000 Reichmarks ‘donation’, to be split between the two teams, plus 50k of win bonuses, triggered racing’s most heroic age, but they came nowhere near covering the costs of running four- and five-car teams, Avus streamliners, mountain-climbers and record-breakers for six seasons. Meier could not have known it, but he was sitting in a car the build quality of which would only be surpassed deep into Formula 1’s carbon-fibre era. Auto Unions didn’t come cheap — and the contemporary Mercedes probably cost twice as much; whereas its rival might employ a solid balljoint in the steering assembly, Stuttgart would utilise one twice as big — and then hollow it out! A 1970s F1 car is Fisher Price in comparison.

But Zwickau — Auto Union’s race shop was based at Horch’s factory there — didn’t spend for spending’s sake. Its new V12 bore striking resemblances to the original V16: a central cam operating both banks of inlets, the same conrod length and main bearing diameter. Necessity is the mother of invention, however, and the packaging advantages of the Auto Union’s layout allowed it to compete with the more complicated Mercs.

Some big changes, though, couldn’t be avoided, and Eberhorst got rid of two bones of contention: cab-forward seat position and rear swing axles. The latter had imbued the cars with better traction and straight-line stability than its live-axled rivals, but at a cost. Porsche’s design incorporated independent suspension front and rear: his twin-trailing link, transverse-torsion bar front — which the D-type retained — has a low roll-centre; his swing-axle rear (torsion bars replacing transverse leaf spring in 1935) has a high roll-centre. This was a fractious marriage in a car with a relatively high CoG, jerky friction dampers and a driver far removed from his usual ‘comfort’ zone. In a bid to install some stability and control, extremely stiff spring rates were employed — and thus we were almost back to where the process had begun.

Matters improved when Mercedes, which had also utilised swing axles, adopted a de Dion tube rear end in 1936. This was no panacea, as evinced by the superiority of Auto Union’s secret weapon of that year, ZF’s limited-slip diff, but it gave much better control of the rear wheels, while the subsequent loss of independence was compensated by its introduction of more consistent, more adjustable hydraulic dampers — and softer springing — in ’37.

Eberhorst went the same route with the D-Type, stepping its de Dion tube under the gearbox and locating it laterally via a low-mounted Panhard rod. It was a neat and simple design, the tube being an arc-welded fabrication rather than pieced together from several forgings as on the Mercedes — and it provided a low roll-centre; the D-Type had found its balance. Eberhorst fitted piston-type hydraulic dampers, too, albeit with the belt-and-braces approach of retaining the friction jobs at the rear. The result of all this change was that the D-Type was a basic understeerer.

What has separated the great from the good in every era of the sport (ever more so as grip levels have increased, admittedly) is the speed a driver can carry into a corner without overly compromising his exit, for this is by far the most difficult skill to master. Oversteer could be called up at will in the 1930s, but several photographs of Nuvolari in Alfas show him turning-in early, carrying speed, while adopting an understeering stance. That’s probably why he adapted so well to the D-Type, scoring three of its four victories: Monza and Donington in ’38, Belgrade in ’39.

The D-Type’s handling was a big step forward. It was no pussy cat, though. There was no getting away from all that power and narrow, rock-hard contact patches. Oversteer was still a flex of the ankle away at all times — and in all gears. Meier set the fastest time of the all the ‘hopefuls’ gathered at the Sudschleife and was signed up for 1939, but he had found the car hard work, heavy to steer and tricky to control near the limit; he had spun on three or four occasions.

I have neither the intention nor capability of repeating Meier’s performance, but I can concur with his assessment of the steering. This worm-and-nut arrangement takes plenty of muscle at low speed; core strength, too — pecs and abs as well as shoulders, biceps and forearms. No wonder Nuvolari was wiry. The cramped cockpit — 44 inches from seat back to wheel boss — and upright seating position suddenly make sense, without becoming any more comfortable. The in-your-chest tiller, adjustable for rake, had initially seemed like an overly keen bouncer desperate to usher you off the premises; in fact, he’s just trying to help you find your way. Wheel-twirling is reduced by high-geared steering which, at approximately a turn from lock to lock, is positively go-kart. Rapped knuckles must have been a regular occurrence even so, the gap between the cockpit surround and wheel rim being little more than a finger’s width.

Temperatures and confidence increasing after a few runs down and up, it’s time to be a bit braver. There is a wide apron of Tarmac at the top of the rise and I swing hard right. The nose drifts slightly wide and I feed in the power. Don’t kid yourself that the light section of the throttle travel is just play — it’s responsible for the first 3000rpm, which is enough to tighten the circle, the inside-rear just starting to climb up onto the diff’s locking action. Next time, I shove past ‘the play’ and the tail comes around, progressively. And along with it comes a smidge of opposite lock. It’s surprisingly well-balanced and well-behaved.

I’m acutely aware that this is far removed from a 140mph four-wheel drift on the cobbled, downhill right-hander past the pits at Berne, but as Mark Donohue would later prove, you can learn a lot from ‘skidpan’ work. And Captain Nice would have approved of the D-Type’s 45:55 weight split, its (relatively) low CoG, and low polar moment of inertia courtesy of the central siting of its fuel tanks. This latter item was a major design consideration: the 63-gallon load was almost 15 per cent of its all-up weight; the Mercedes carried 88 gallons, a great deal of which hung over and beyond its rear axle. You don’t have to be Colin Chapman to see which needed driver-adjustable dampers to cope with the dramatic handling changes caused by such huge, fast-draining tanks.

The acid test for me, Captain Nice-and-Steady, is that I’m now wishing we were out on the modern Donington Park. Never in my wildest dreams had I expected to feel this way; the D-Type is more ‘understandable’ than I ever thought it could be. But should that be a surprise given that it’s mid-engined with side fuel tanks and an air intake behind your head, and that you sit in it rather than on it with your backside almost precisely amidships? There is a lot here that is way ahead of its time. Daunting from without, the car ‘shrinks’ considerably once aboard. Driving position aside, it feels right.

What a thrill it must have been to hear these engine notes echo through the woods and bounce off stone gable-ends before a Silver Arrow burst into view going in several directions at once. 200mph feels fast on a wide banked oval — imagine it on a two-lane Route Nationale with man of the moment Hermann Lang on your gearbox. My God! Even at Donington Park, which at a little over three miles was considered Mickey Mouse — no overtaking through the middle arch of the Stone Bridge or the farmyard at Coppice! — speeds were in excess of 170mph on a main straight that was very narrow, undulating and far from straight.

They must have braked before the crest at the beginning of the Loop, for not only is there a sharp descent, there is a distinct kink right, too. A blind apex had to be clipped here, and at the return-leg left, if a grassy landing was to be avoided. In 1938, the German cars did not aviate as grandiosely as had the more powerful machines of ’37, but Manfred von Brauchitsch and Nuvolari were only half a second shy of the former’s previous pole time, in cars half the capacity. Had they returned the next year they would have bettered it.

My day at Donington is curtailed by a chill wind and dislike of tow starts — beautifully crafted nose too close to van rear doors for comfort. But I have seen, heard and felt enough to know that Auto Union was perhaps a season away from dispelling the myths about mid-engined design. The 1500cc supercharged formula mooted for 1940 and beyond — smaller and better-packaged cars please apply — would have played right into its hands. Sure, Mercedes had stunned its rivals with the 1.5-litre W165 — a jewel of a machine — it built to win the ’39 Tripoli race after the Italians had changed its formula late in the day, but would its successor have been mid-engined?

I think yes — if it had wanted to win regularly.

Technical specification

Engine

Type and construction: twin-stage supercharged 60deg V12; three gear-driven cams; two-valve, singleplug heads 90deg included angle; one-piece aluminium crankcase and block, forged-steel wet liners; Mahle forged four-ring pistons; Hirth built-up crankshaft, roller bearings Capacity: 2985cc Bore x stroke: 65 x 75rnm Compression: 10:1 Max power: 485bhp @ 7000rpm Max torque: 4051b ft @ 4000rpm Bhp per litre: 95.48 Carburation: Solex, two twin-choke (SUM, `waterfall’-type in 1939) Fuel pumps: Bosch Mpg: 2.75 Ignition: Bosch, two magnetos Superchargers: Roots-type, Elektron, (large) 2.25 litres per revolution, (small) 1.2 litres, both running at 1.63 times engine speed Boost: 24psi

Drivetrain

Gearbox: 5-speed plus reverse, twin-shaft Differential: ZF, limited-slip, spiral bevel Clutch: twin-plate

Chassis

Construction: chrome-molybdenum tube main frame (145mm) and cross-members (65mm) Frame weight: 51kg Wheelbase: 2850mm Length/width/height: 4200/1660/1060mm Track: 1390mm Weight: 850kg Suspension (f): independent, Porsche twin-trailing link, transverse torsion bars, hydraulic dampers Suspension (r): de Dion, Panhard rod, single radius arms, transverse torsion bars, hydraulic and friction dampers

Running gear

Steering: worm and nut Brakes: Lockheed, 17-inch drums, four leading shoes Fuel capacity: 62.7 gallons Hubs: Rudge-Whitworth Wheels: 19in (f) 22in (r) on faster tracks: Tyres: Continental (Dunlop now), 6 x 19in (f), 7 x 19in (r)