New Audi A8 50 TDI Quattro vs. Mercedes S 350 d: Diesel engines in the luxury class

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Even after four generations and a quarter of a century since the launch of the original model, the new Audi A8 50 TDI Quattro is still the challenger of the establishment, going against the Mercedes S-Class. FIRST COMPARISON TEST.

Never let her see how hard you try. Only when the audience understands power, brilliance or state-bearing grandeur, it all seems sovereign. Yes, this is about the eternal war between the A8 and S-Class, and to understand what the two contenders are, we need to understand where the two cars are coming from. The Mercedes namely from nowhere, it was always there. Since the rich, the beautiful, the powerful belong to the circles that a Mercedes moves – a status that every S-Class inherits and that you can not develop. It is developing.

At Audi they try to break this mold since the first A8 from 1994 to compensate for the alleged deficit in the status with Vorsprung durch Technik. So the fourth generation of the A8 drives up a lot of innovation.

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From tradition to revolution
This is less evident in the design style, which should not shake even traditionalists. When it comes to revolutions, Audi does not focus on outside but on the inside. The aluminum frame, the Space Frame, is a multi-material construction made of aluminum, magnesium, steel and CFRP. This increases Audi torsion resistance by 24 percent, but reveals the unique feature of the Space Frame – the desire to build the lightest sedan in the class. Even so, the A8 50 TDI Quattro weighs only 14 kg less than the S 350 d 4Matic.

But it fits to the A8, to set itself always new goals. First it wanted to be the lightest luxury liner, later the sportiest, now the most innovative. That’s why the comparison test also begins in the flickering light of the neon tubes in our underground car park. There is so much to set in the Audi, that does not work until the actual test ride.

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Audi has sorted out the MMI control dial. But that does not mean that the new operating architecture is better. Because now you can astonishingly fast and intuitive run your fingers through the menus on the two superposed touch-sensitive monitors. When pressed, the display is minimally moved to give the finger a confirmation pulse, a loudspeaker plays a clicking sound. You think that is a big digital effort to imitate something analog? We do not want to contradict that. Mostly because these heavy metal knobs left the previous A8 feeling solid enough not to be leased, but inherited. This may no longer happen while the climate control is trying to wrap you around with your little touching and sliding surfaces around your finger.

When stationary, this is still possible, but during the ride, the ergonomy distracts sharply – too profoundly and nested menus. If Audi says the operation means a new user experience, that may be true. But a real step forward would have been to sort out everything in terms of operation, which one never suspends anyway, so to make a selection of the relevant, rather than amassing what is available.

However, the ergonomy of the S-Class is also not far more intuitive – due to fussy swipe buttons on the steering wheel for the on-board computer, assistance and Navi and the complicated combination of turn-pusher controller and the small touch surface above. So, now press the start buttons. In the S-class self-ignites the new inline-six cylinder engine it got the with the facelift in the summer.

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The foundation of its power is the 600 Nm torque – from 1,200 rpm. Since it delivers all 286 hp at 3,400 rpm, revving is not the topic for this diesel. Instead, it rests on the early strength. Thus, the S 350 d builds a vehement pace with serenity, reacting sovereignly instead of sensitively to the gas pedal impulses. Meanwhile, the automatic gearbox switches softly and relaxed through its nine stages.

That fits, yes, actually to everything about the S-Class and the majesty it conveys. At the end of the hood, the star stretches towards the horizon, towards which the car rushes. At the same time, the air suspension keeps the filthiness of wrinkled streets away from the occupants, does not wobble a bit, even on short, hard bumps. Here the S is in a class of its own.

It would not be surprising if the Mercedes did not like being handled fast. So we are not surprised that it responds to direction changes calmly, in the pursuit of high driving safety without great ambitions of precision from the indirect steering.

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Voluminous, but not as sublime as expected, material and processing quality is high, the brakes strong, but not as vehement as that of the Audi, the engine efficient, but not so economical – there are some points in which the S-class shows its age. This is even true for the assistance equipment, which is not as extensive as that of the Audi and not entirely reliable.

The A8, now more sporty than ever
The urge for perfection drives the A8. And of course, the V6 TDI, which Audi combines to increase efficiency with a 48 volt mild hybrid. Whereby it is not about boosting the three-liter diesel – there is no reason to with 600 Nm and 286 hp on hand, but the faster power development and the more vigorous eight-speed automatic, which reacts faster than the transmission of the Mercedes.

The 48 volt system consists of a 10 Ah lithium ion battery and a belt starter generator mounted on the crankshaft. From these comes the energy to keep all systems running when the A8 is in deceleration between 55 to 160 km / h for up to 40 seconds with the engine decoupled. The savings potential shows in the test consumption of 7.6 l / 100 km – this is remarkably little and makes the 8.0 l / 100 km of the S 350 d seem almost greedy.

Optionally Audi offers the fully networked AI chassis that controls each wheel individually by electromechanical actuator load and in an impending side crash lifts one side of the car by eight inches. The test car came with the standard suspension, while the Mercedes is equipped as standard with the air suspension. The A8 brings a firmer ground set-up, responds to short bumps, controls body movements even better – in each of the driving modes. The A8 always stays alert, leaving the cuddly S-Class behind.

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As with its group colleague Porsche Panamera, Audi has four-wheel steering. With parallel rear wheels, it boosts stability when changing lanes on the freeway and in fast corners. In tight bends, the rear wheels deflect in opposite directions, increasing agility and maneuverability. In fact, because of the good all-round visibility on the road, it does not feel as if it were necessary to turn a 2.1-tonner with 10.1 square meters of ground. Instead, the Audi looks much more compact, bends determinedly, but not abruptly in curves, it circles around neutral, fast, very safe and expresses itself powerfully. The perfect traction is ensured by the all-wheel drive, which sends 60 percent of the power to the rear axle during normal driving. The steering feedback fits. Now the A8 gives clear indications of what is going on with the front wheels without letting go of any asphalt granules or tangling with bumps.

We should mention the excellent brakes and the brilliant LED lights and the very comprehensive assistance equipment.

Little things only? Well, that’s precisely what the claim to build the most innovative luxury sedan is about. The A8 finally wins against the sovereign S-class. But it is the very essence of perfection to be out of reach – no matter how hard you try.

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1. Audi A8 50 TDI Quattro
487 points
The perfect sedan is less what the A8 wants to be, showing all its rivals what is currently the best in terms of assistance and infotainment, comfort and handling. The victory seems calculated ingeniously.

2. Mercedes S 350d 4Matic
470 points
The perfect S-Class? It does not want to be less, bragging about the supreme suspension comfort. In the case of handling the backlog may not matter, with safety equipment and brakes a bit behind the times.

Technical Data
Mercedes S 350 d 4Matic Audi A8 50 TDI Quattro
Base price
89.399 € 90.600 €
Lenght x width x height 5125 x 1899 x 1496 mm 5172 x 1945 x 1473 mm
Trunk volume 510 l 505 l
2925 cm³ / 6-Cylinder 2967 cm³ / 6-Cylinder
Power 210 kW / 286 PS at 3400 rpm 210 kW / 286 PS at 3750 rpm
Top speed
250 km/h 250 km/h
0-100 km/h 6,1 s 6,0 s
Consumption 5,5 l/100 km 5,6 l/100 km
Test consumption
8,0 l/100 km 7,6 l/100 km