Even more dynamism
Typically for an Audi, the new S8 likewise focuses on quattro permanent four-wheel drive. As a result it produces superior traction in all surface conditions. 25 years of expertise acquired in this domain by the brand with the four-ring emblem have led to the development of a new quattro generation with asymmetric/dynamic torque distribution – further evidence of Audi's philosophy of "Vorsprung durch Technik".
A centre differential, installed longitudinally in the driveline, distributes power between the front and rear wheels according to the prevailing situation. Normally, 40 percent is routed to the front wheels and 60 percent to the rear, this slight emphasis on the rear underlining the dynamic character of the Audi S8. If the surface conditions change, the purely mechanical differential responds without any delay; it can divert up to 85 percent of power to the rear wheels, and as much as 65 percent to the front wheels. If a wheel on one axle spins, it moreover overrides the Electronic Differential Lock EDL by applying the brakes.
The new S8 is equipped with six-speed tiptronic as standard. In keeping with the character of this saloon model, the final ratio of the automatic transmission is lower than on the A8 – the saloon is still capable of forceful acceleration even in sixth gear. The electronic transmission control is optimised to change gear more dynamically. The driver can call up the transmission's Sport mode via the selector lever – it still performs upshifts even at relatively high engine speeds. It is in addition possible to change gear manually with the shift paddles located behind the steering wheel.
For Audi, lightweight design is a philosophy that has implications for every area of a vehicle. The V10 in the Audi S8 weighs in at a mere 220 kilograms, in other words 20 kg less than an equivalent competitor engine. Good axle load distribution and impressive road behaviour are the result. For the same reason, the batteries and the energy management are housed in the luggage compartment.
Built for serene speed
The basic version of the Audi A8, adaptive air suspension, already possesses distinctly sporty attributes thanks to its elaborate layout. The control arms are made from aluminium; the front suspension consists of a four-link structure, and there is self-tracking trapezoidal-link rear suspension. Various details of this layout were revised on the S8.
The basis is "adaptive air suspension sport", the sports suspension layout that is available for the A8 as an option. On the S8, the characteristics of the air springs and the shock absorbers integrated into the air-spring bellows have been made somewhat firmer. With a further reduction in rolling and pitching movements, the sporty top model behaves with even greater agility and manoeuvrability, but is as stable and safe as ever. The elastokinematics of the rubber mounts in the axles have likewise been modified in keeping with the character of the S8. The variable steering ratio is roughly ten percent more direct, for even more spontaneous handling.
Drawing information from seven special sensors and a number of other parameters, the damping responds adaptively to the prevailing requirements in a fraction of a second. Its control system features four driving modes – automatic, comfort, dynamic and lift – which the driver can call up via the terminal of the MMI operating system. The body's ride height is as envisaged in conjunction with adaptive air suspension sport, which is already 20 mm lower than standard. On the S8, ground clearance is varied in three stages between 125 mm in the comfort mode and 95 mm at constant high motorway speeds.
The Audi S8 is equipped ex works with S-design cast alloy wheels. Their dimension is 9J x 20, and the wide tyres are size 265/35. An 18-inch brake system assures a superlative braking performance. It features four large-size ventilated brake discs. The brake calipers are painted black, and adorned with a titanium grey S8 badge at the front. The discs on the front wheels measure 385 millimetres in diameter, and 335 mm at the rear.
The optional ceramic brakes that also became available for the twelve-cylinder A8 in summer 2005 are a further special feature of the S8. They are made from a composite material comprising high-strength carbon fibres embedded in hard, frictionally resistant silicon carbide. The ceramic discs offer significant advantages compared with conventional steel discs. They are about half the weight, are largely insusceptible to heat fading and corrosion, and achieve an operating distance of up to 300,000 kilometres – four times that of steel discs. Optically, the high-tech brake system can be identified by the special perforation on the large-size discs and the anthracite-coloured calipers with the "Audi ceramic" lettering.