By Audi Media
Great precision, supreme stability, sporty character and excellent ride comfort: The chassis of the new Audi A8 combines many strengths. The adaptive air suspension and Audi drive select are standard, with dynamic steering available as an option.
With a track of 1,644 millimeters (64.72 in) the front axle comprises five links – two transverse links, the support link and the control arm plus the track rod. All wheel control arms and many other parts, such as the bearing mount and the pivot bearing, are made of aluminum The five-link design can handle longitudinal and lateral forces separately. Its bearings are sportily stiff in the lateral direction and supple and soft in the longitudinal direction.
The subframe for the suspension and the engine is made of high-strength steel and reinforced with X-shaped braces. 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 aluminum strut brace further enhances the rigidity of the front of the car.
Among the additions to the Audi A8 is the electromechanical rack-and-pinion steering. Unlike a hydraulic unit, it requires energy only while turning, thus reducing fuel consumption. The steering gear ratio of 16.1:1 is sporty and direct, and steering boost varies as a function of vehicle speed. The assistance systems Audi active lane assist and park assist would not be possible without the steering system’s electromechanical drive.
The electromechanical steering provides finely differentiated feedback from the road, responds spontaneously and is very precise. The steering gear is mounted very low, on a level with the center of the wheel. The track rod forces are applied directly. The steering rack and the servo drive are arranged in concentric circles for a very compact layout.
The rear axle of the new A8 has a track width of 1,635 millimeters (64.35 in) and is a track-controlled trapezoidal link construction that ensures supreme handling and comfort. The two trapezoidal links are warm-hardened aluminum castings; the transverse links and track rods are aluminum forgings.
The struts act directly on the wheel carriers, which are chill-cast aluminum. This solution allows a high damping ratio and thus sensitive response. The rear axle subframe comprises steel longitudinal and transverse tubes. Four hydraulic bearings connecting the subframe to the body also greatly contribute to the ride comfort.
The adaptive air suspension: Sensitive suspension
All versions of the new Audi A8 come standard with the adaptive air suspension regardless of the engine. The air supply unit is located in the rear of the car, where the compressor fills a pressure accumulator with a volume of 5.8 liters (0.20 cubic ft). The pneumatic struts enclose adjustable, two-tube shock absorbers whose performance can be adjusted by the millisecond via the control current for the electromagnetic damper valves. Supplied with data from a complex system of sensors, the damper management system detects the road conditions, the driver’s style and the mode specified in Audi drive select.
The five modes the driver can select their for the adaptive air suspension influence body’s ride height. In auto mode, the superstructure is lowered 20 millimeters (0.79 in) when the A8 drives for longer than 30 seconds at over 120 km/h (74.56 mph). The body is not lowered in comfort mode. In dynamic mode, on the other hand, the body is lowered 10 millimeters (0.39 in) from the outset, and is lowered another 10 millimeters when the 120 km/h (74.56 mph) threshold is reached. In efficiency mode, numerous systems work with particularly little energy, and the fifth mode, individual, gives the driver the opportunity to adapt the system within certain limits to his or her preferences. Another special feature is the lift function, which increases ground clearance by 25 millimeters (0.98 in). The optional adaptive air suspension sport lowers the standard ride height by 10 millimeters (0.39 in).
Audi drive select opens up a wide range of possibilities for the driving experience in the new Audi A8. In the standard version, it integrates the adaptive air suspension, the eight-speed tiptronic, the electromechanical power steering, Audi pre sense basic, the engine control unit and the air conditioning. The driver can vary the function of these components between the modes comfort, auto, dynamic, efficiency (not in the A8 hybrid) and individual.
The optional modules sport differential (standard in the A8 4.2 TDI and the S8), ACC stop&go, dynamic steering and the accelerator characteristic can also be controlled via Audi drive select.
At the heart of the dynamic steering system is a superposition gear that varies the steering ratio by nearly 100 percent as a function of driving speed and the setting in Audi drive select. When maneuvering and in city traffic, the system is very direct. On the highway, an indirect steering ratio and less boost promote straight-line stability. At the vehicle’s cornering limits, dynamic steering minimizes oversteer and understeer by making subtle, lightning fast adjustments, if necessary. It also counteracts the car’s pulling to one side when braking on surfaces with different coefficients of friction.
The brake system: Lightweight construction and high performance
The brake system of the new Audi A8 is powerful and robust, yet lightweight. Stainless steel pins connect the cast iron friction rings to the aluminum brake caps. This concept prevents the transmission of temperature peaks, reduces the risk of fade and cuts up to four kilograms (8.82 lb of weight). The very high rate of ventilation made possible by the turbine design of the cooling channels between the discs enhances braking performance.
Disc diameter varies depending on the engine, measuring 365, 380 or
400 millimeters (14.37, 14.96 or 15.75 in) up front and either 330 or 356 millimeters (12.99 or 14.02 in) on the rear axle. The brake caps and calipers, which have two pistons each up front and one in the rear, are painted black. For the W12 and the V8 versions, Audi optionally supplies large brake discs made of carbon fiber ceramic. They are even lighter than the steel discs and are extremely durable.
The ESC electronic stabilization control system includes a sport mode, which the driver can select in the MMI. Engine intervention is largely deactivated in this case, and braking interventions are weakened somewhat, enabling skilled drivers to move the sedan particularly dynamically. The electromechanical parking brake in the new Audi A8, which acts on the rear wheels, also serves as the emergency brake. Audi hold assist makes it easier to start out on uphill and downhill slopes.
There is a large range of alloy wheels. V6 models roll on 17-inch wheels and size 235/60 tires. With the V8 models, these dimensions are 18 inches and 235/55. Additional wheels and tires from 18 to 20 inches in diameter (21 inches with the S8) in modern designs, including two-tone and titanium-look finishes, are available as options. Run-flat tires are available for the 19-inch wheels. The winter tire lineup ranges from 17 to 20 inches. A tire pressure indicator is standard.
New in the lineup are 9 J x 20 aluminum technology wheels manufactured using an innovative cladding technology. A forged aluminum carrier wheel forms the basis. Its design with the ten slender arms has been optimized for minimal weight. Only slight consideration need be paid to wall thicknesses and cross-sections during casting. A special foam permanently bonds the carrier wheel to a design element of high-impact, injection-molded polymer, which also features a ten-spoke design. The foam fills the cavities and is extremely resistant to heat, which is important with powerful braking.
The new aluminum technology wheel underscores Audi’s claim to leadership in lightweight construction. Besides the great design freedom, it also reduces the car’s unsprung masses substantially. Its innovative structure saves 4.35 kilograms (9.59 lb) compared with a conventionally fabricated forged wheel of the same design. That means a total weight reduction per car of 17.4 kilograms (38.36 lb). Its surfaces in Iridium/Contrasting Gray emphasizes the three-dimensional effect and gives the new A8 wheels with an exclusive and unique look.