The Audi S8 is the dynamic top model of the A8 family, combining the comfort of a luxury sedan with amazingly sporty handling. Its sophisticated chassis combines high precision with supreme stability and an excellent ride.
All wheel control arms and many other components are made of aluminum. The track measures 1,644 millimeters (64.72 in) up front and 1,635 millimeters (64.37 in) at the rear. The front suspension comprises five links per wheel – two transverse links on the upper plane, the support link and control arm in the lower plane, and the track rod.
The five-link design can handle longitudinal and lateral forces separately. Their bearings are stiff in the lateral direction, enhancing sporty precision; on the other hand, the bearings are remarkably pliable in the longitudinal direction. The axle links are aluminum forgings; they keep the unsprung masses low. The anti-roll bar fabricated from a high-strength tube also saves weight.
Made of high-strength steel and reinforced with X-shaped braces, the integral subframe for the engine and the front axle forms the backbone of the suspension. Because it is rigidly bolted to the front end of the car, it becomes an integral component of the body. The high rigidity ensures that steering forces develop without delay. A diecast strut brace further enhances the rigidity of the front of the car.
The rear suspension of the new S8 follows the track-controlled trapezoidal link principle, a compact design that ensures superior driving and comfort qualities. The two trapezoidal links are warm-hardened aluminum castings; the wheel carriers are of chill-cast aluminum. The top transverse links and the track rods are aluminum forgings; the stabilizer bar is also a tube.
The struts act directly on the wheel carriers. This allows a high damping ratio so that the dampers react sensitively. The developers were also able to redesign the axle beam bearings to be more comfortable. The beam comprises two steel longitudinal and lateral beams each; four hydraulic bearings connect them to the body.
Versatile: the adaptive air suspension
The new Audi S8 comes standard with a tautly tuned adaptive air suspension, which combines a high-end air suspension with controlled damping and is also used to level ride height. The air supply system is located in the rear of the car. The compressor works with a pressure of 18 bar and fills a 5.8-liter pressure vessel. The large air capacity of the struts allows a soft characteristic and fine response even without an auxiliary accumulator.
The adjustable two-tube shock absorbers inside the struts are characterized by their low friction. Supplied with data from a complex system of sensors, the control unit adapts the function of the shock absorbers to the road conditions, the driver’s style, and the mode specified in the Audi drive select system. Individual adjustments for each wheel are made continuously by the millisecond via the control current for the damper valves.
The driver can choose between four different modes for the adaptive air suspension in Audi drive select. Changing modes changes the response of the shock absorbers and the ride height, which is already ten millimeters (0.39 in) lower than on the Audi A8. In auto and dynamic modes, the body is lowered by a further 10 millimeters (0.39 in) once the S8 has driven longer than 30 seconds at a speed greater than 120 km/h (74.56 mph). This increases stability and reduces drag, thus saving fuel. In lift mode, ground clearance increases by 25 millimeters (0.98 in) from the standard ride height so that smaller obstacles can be overcome.
The standard Audi drive select system makes driving an even more versatile experience. In addition to the adaptive air suspension, it also integrates engine management, the eight-speed tiptronic, the dynamic steering, the sport differential, the ambient lighting and the Audi pre sense basic safety system.
The driver can vary the function of these components between the three modes comfort, auto and dynamic. Drivers can – within certain limits – also compose an individual mode corresponding to their own personal preferences. The fifth mode, efficiency, promotes an economic driving style. In this mode, Audi drive select also controls the deluxe automatic air conditioning and the ACC with stop&go function accordingly.
Variable ratio: dynamic steering
Dynamic steering is also standard in the Audi S8. It is extremely precise and delivers sensitive feedback. It uses a superposition gear known as a harmonic drive to vary the steering ratio by nearly 100 percent as a function of driving speed and the setting in Audi drive select. In city traffic it is very direct; at highway speeds it is indirect to avoid unnecessary constant steering adjustments.
At the cornering limit, the dynamic steering helps the driver to cancel out understeer and oversteer by performing tiny steering corrections autonomously. It also prevents the car from pulling to one side when braking on surfaces with different coefficients of friction. The system needs less time for such corrections than the brake system needs to develop pressure at the wheels. In many cases it does most of the work virtually unnoticed by the driver.
The hydraulic dynamic steering system receives its energy from a regulated vane-type pump, which provides only as much fluid as is required at any specific moment. The steering gear, a rack-and-pinion construction, is mounted on the subframe down low and far to the front. The track rods communicate the steering input very directly to the wheels.
The Audi S8 comes equipped with a powerful, durable and lightweight brake system. All discs are internally vented; the front discs are also perforated. Stainless steel pins connect the cast-iron friction rings to the aluminum brake caps – a concept from sports car design that prevents the transfer of temperature peaks, reduces the risk of fading and reduces weight.
The front discs measure 400 millimeters (15.75 in) in diameter; the rear discs 356 millimeters (14.02 in). Six-piston calipers painted matt black and sporting S8 logos are used up front, with single-piston calipers at the rear. Audi offers carbon fiber-ceramic discs with anthracite gray calipers as an option. They are particularly robust and durable, and together they are roughly 13 kilograms (28.66 lb) lighter than steel discs.
The ESP stabilization system is state of the art and works closely together with the dynamic steering, the sport differential and the adaptive dampers. The ESP in the S8 includes a sport mode, in which the system intervenes significantly later. A trailer stabilization system and tire pressure indicator are also standard. Another standard feature, the auto release function, facilitates starting off on hills.
The wheels of the S8 feature a five parallel-spoke design, typical of the S models from Audi. They measure 9 J x 20 and are fitted with 265/40-series tires. Audi offers five additional wheels as options, four of which measure 21 inches in diameter. They come in a choice of attractive designs: polished, high-sheen or two-color. Winter wheels are available in 19 and 20 inch sizes. A tire repair kit comes standard; a space-saving spare tire is available for no additional charge.
The equipment, data and prices specified in this document refer to the model range offered in Germany. Subject to change without notice; errors and omissions excepted.