The new Audi A8 is the sportiest sedan in the luxury class – and its chassis is largely responsible for this. It combines uncompromising precision with great dynamism, superior stability, and excellent comfort. The adaptive air suspension including controlled damping and the Audi drive select dynamics system comes standard, with Audi offering dynamic steering as an option.
Even when standing still the new A8 clearly expresses its most important trait: The wide track, the large wheels and the long wheelbase convey a powerfully sporty image. In motion the large sedan impresses with its sprightly agility. The A8 steers spontaneously and willingly, remains nearly neutral at the limit and finds strong traction when exiting curves thanks to the power delivered to all four wheels.
Shifted forward: the front axle
The Audi engineers shifted the five-link front axle forward by 145 millimeters (5.71 in) compared to the previous model. The result is a well-balanced distribution of vehicle weight between the front and rear axles, with the rear-axle differential in the quattro drivetrain and the battery located in the trunk contributing to this balance. The 1,644 millimeter (64.72 in) front track of the new Audi A8 is far wider than those of its competitors.
The integral subframe for the engine and the front axle, which is made of high-strength steel and is reinforced with X-shaped braces, forms the backbone of the front suspension. Because it is rigidly bolted to the front end of the car, it becomes part of the body. The high rigidity ensures that steering forces develop without delay.
The bearing pedestal, which is likewise integrated into the body and connects the upper control arms, and the pivot bearing are made of aluminum. A complex casting process ensures that the bearings are of the highest strength yet low weight. A monolithic, die-cast strut brace connected to the body at seven points further improves the rigidity of the front of the car.
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. All suspension control arms are forged aluminum parts, guaranteeing low unsprung masses, extremely precise wheel location and safe crash behavior. The anti-roll bar fabricated from a high-strength tube also saves weight.
The five-link suspension can handle longitudinal and lateral forces separately. The bearings are rigid in a lateral direction to promote sporty precision. In the longitudinal direction, on the other hand, they have a supple, soft response thus unifying the dynamism of a sports sedan with the comfort of the luxury class.
The kinematics of the front suspension offers major advantages. They allow the camber and caster angles to be selected for precise centering of the steering when driving straight ahead, ensuring the sense of steering accuracy around the straight-ahead position. The arrangement of the control arms makes it possible to reduce the leverage exerted by driveline and external forces, so that the driver does not feel them at the steering wheel.
Precise and sensitive: the steering
The steering system used on the previous model was also extensively revised. The steering gear, which used to be installed on the bottom of the radiator tank, is now placed low and far to the front, below and in front of the center of the wheel on the subframe. The steering impulse is introduced with great directness into the wheels through the track rods. Friction-optimized track rod joints increase the precision of the spontaneous response. The wheel bearing, which is also of a special low-friction design, has a large diameter of 102 millimeters (4.02 in) that reduced the specific load, thus increasing service life.
The steering column is bolted in a rotationally fixed manner to the module crossmember below the windshield frame and the bearing pedestal of the bulkhead. The steering column dissipates energy in the event of a frontal collision, and a telescopic shaft prevents it from penetrating the cabin. It has also been optimized with respect to its eigen frequency.
The steering gear is a rack-and-pinion design with a casing of lightweight die-cast aluminum. With a ratio of 16.1:1, the steering is sporty and direct, communicating precise and finely differentiated feedback from the road in any situation. A controlled-output vane-type pump supplies the necessary hydraulic energy; unlike conventional power-steering pumps, which circulate a large volume of oil internally, it delivers only as much oil as is needed at any given operating point. This reduces the fuel consumption of the new Audi A8 by 0.1 liters/100 km.
All A8 versions leave the factory with servotronic power steering, which adapts its power assist to the speed being driven to further enhance both comfort and the sporty character. The steering is precise in all situations while at the same time communicating finely differentiated feedback from the road.
Dynamics and comfort: the rear suspension
Major elements of the rear suspension of the new Audi A8, which has a track of 1,635 millimeters (5.36 ft), have been redesigned. Designed according to the track-controlled trapezoidal link principle, it combines compact design with superior performance and comfort qualities. The overall kinematics greatly suppress dive and pitch while braking and accelerating, which also enhances the sporty dynamics.
Unlike in the previous model, the struts no longer rest against the upper transverse links, but rather directly on the wheel carriers. This allows a 30 percent higher damping ratio so that the dampers react with greater sensitivity. The developers were also able to redesign the axle beam bearings to be more comfortable. Elastic bearings connect the wheel control arms to the axle subframe. With their high damping rate rubber mixtures, they play a major role in bringing comfort and dynamics together.
The developers also kept the unsprung masses as low as possible at the rear axle. The two trapezoidal links in the form of hollow sections are warm-hardened aluminum castings; the wheel carriers are of chill-cast aluminum. The top transverse links and the track rods are aluminum forgings. Their high rigidity ensures that toe and camber angles change very little when dynamic forces act on the wheels. The stabilizer bar, which is also tubular, also combines great rigidity with low weight.
The bending and torsionally rigid subframe comprises two longitudinal and two transverse tubes of higher-strength steel shaped using extremely high water pressure. Four hydraulic bearings connect the subframe with the body. They are particularly firm in the transverse direction for sporty handling, but have a soft response vertically and longitudinally in the interests of comfort.
Incredible range: Audi drive select
Audi drive select lends an incredible range to the experience of driving in the new A8 – from highly comfortable to sporty and taut. It integrates the adaptive air suspension, the engine, the eight-speed tiptronic, servotronic and Audi pre sense basic. The system modifies the characteristics of the air springs, dampers, and the accelerator, and adapts the shift points, steering boost, and the trigger time for the reversible belt tensioners.
With the MMI the driver can change the characteristics of these modules between the comfort, auto, and dynamic modes at any time via the “Vehicle settings” menu. All adjustments are made safely and harmoniously; they make their presence known, but do not irritate. You can also compose your own “individual” mode – within certain reasonable limits – corresponding to your own personal ideal by choosing settings from the portfolio.
Audi drive select proves to be extremely versatile in the new A8. Customers can order a series of additional driving dynamic and lighting modules. Two optimal components in terms of driving dynamics are already available – the sport differential for the variable distribution of power between the rear wheels and dynamic steering.
Variable gear ratio: dynamic steering
Dynamic steering is a high-end feature that varies the steering ratio by nearly 100 percent as a function of driving speed and the setting in Audi drive select.
The central component is a superposition gear integrated into the steering column and driven by an electric motor – a harmonic drive originally developed for robotics and space flight applications. The unit is compact and light and reacts free of play, precisely, and with low friction. The harmonic drive can transmit immense amounts of torque and is very efficient.
The steering is extremely direct at low speeds, such as in city traffic and when maneuvering. The power assist is also high, making it very easy to maneuver the car into a parking space. At moderate highway speeds, the system becomes less direct and provides less power assist. At fast highway speeds, an indirect steering ratio and low level of power assist facilitate steady tracking.
The dynamic steering system cooperates closely with the ESP stabilization program in the sportiness and safety areas. It even countersteers if necessary.
In most situations, its subtle interventions, which the driver often does not even notice, result in a load change that reduces understeer or oversteer as necessary. When the brakes are applied on surfaces with different coefficients of friction, the system actively intervenes with stabilizing steering maneuvers so that track offset, stopping distance and the amount of countersteering required from the driver are minimized.
The dynamic steering needs less time for its corrections than the brake system needs to develop pressure at the wheels. In many situations it does most of the work and there is no need for the braking maneuvers or they serve only as damping to reduce speed. This increased driving safety and sportiness is particularly pronounced when driving at higher speeds on a slick substrate such as snow.
Sporty and very comfortable: the adaptive air suspension
The A8 comes standard with the very comfortable and yet sporty adaptive air suspension. When integrated into the Audi drive select system, this combines a high-end air suspension with controlled damping. It takes ride comfort to a whole new dimension – the new A8 reacts to irregularities in the road surface smoothly and confidently.
The air supply for the adaptive air suspension is located in the rear of the A8. The extremely quiet compressor generates 18 bar of pressure and fills a 5.8-liter cylindrical pressure vessel of aluminum. Control from the pressure reservoir substantially accelerates the level regulation processes.
There are many improvements that enhance comfort. The struts have been newly developed; their increased air capacity now allows a soft characteristic even without an auxiliary accumulator and a fine response even to slight irregularities.
Audi developed all of the damper control software algorithms internally. The driver can choose between four modes with the Audi drive select system. “Auto” offers balanced properties; damping is particularly soft in “comfort.” In both cases the body is initially set to the standard ride height when starting out.
In “auto” mode, the body is lowered by 20 millimeters (0.79 in) when the A8 has driven for at least 30 seconds at a speed greater than 120 km/h (74.56 mph). This increases stability and reduces wind resistance, thus saving fuel. 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, with the ride height lowered another 10 millimeters when the switchpoint is reached. In the fourth mode, “lift,” ground clearance is increased 25 millimeters (0.98 in) from the standard ride height so that smaller obstacles, such as unfavorable ramps, can be overcome. This mode can be selected at speeds of up to 80 km/h (49.71 mph) and automatically switches back to the last mode selected at speeds above 100 km/h (62.14 mph).
The adaptive air suspension also serves as a high-tech level control and keeps the body at the ideal ride height at all times. Passengers enjoy a consistently high level of comfort regardless of the load. Audi also offers the A8 with an optional setup that emphasizes dynamics. The adaptive air suspension sport lowers the ride height in standard mode by 10 millimeters (0.39 in).
The friction of the regulated dual-tube shock absorbers, inside which the air springs are located, was reduced by around 10 percent. The CDC dampers (continuous damping control) are hydraulic shock absorbers according to the dual-tube principle with controllable internal valves. 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 by the millisecond and virtually without delay via the control current for the damper valves. When driving quickly though a curve, for example, the computer reduces body roll by selectively increasing the damping force for certain wheels. During braking, it instantly hardens the shock absorbers to reduce dive and shorten the stopping distance. The dampers also effectively support the work of the ESP stabilization program.
Steady and powerful: the wheel brakes
High performance demands composed braking. The new A8 comes equipped with a powerful and durable top-performance brake system that has been systematically designed for high heat dissipation and low weight.
The front and rear brake discs are internally ventilated. The front axle of the new A8 features discs measuring 356 x 34, 380 x 36 and 400 x 38 millimeters (14.02 x 1.34, 14.96 x 1.42 and 15.75 x 1.50 in). Stainless steel pins connect the friction rings, which are made of a newly developed, high-strength cast iron material, to the lightweight aluminum brake caps – a concept from the sports car segment making its debut in the luxury class.
This reduces the weight and thus the unsprung masses dramatically, by as much as 4.5 kilograms (9.92 lb) depending on the size of the disc. The pins also prevent the transfer of peak temperatures to the brake caps. The elegant pins are visible when the A8 is stationary.
The rear axle of the A8 also sports large, internally ventilated brakes that measure either 330 or 356 millimeters (12.99 or 14.02 in) depending on the engine. The electromechanical parking brake integrated into the calipers is quiet and lightweight.
Safe and agile: ESP
ESP makes a considerable contribution to the agile, sporty character conveyed by the new Audi A8. The stabilization system uses a high-performance, six-piston pump that generates pressure dynamically and controls it precisely and comfortably, free of jolts and perceptible vibrations. The weight of the brake booster has been reduced by 30 percent compared to the previous model.
ESP offers a second mode – the sport mode. In this mode, engine intervention is largely deactivated and brake intervention somewhat reduced so that experienced A8 drivers can drive very dynamically on winding roads.
ESP also offers other functions. For instance, it stabilizes a trailer that is threatening to fishtail by braking the wheels of the A8 in a rhythm opposed to the oscillations. This intervention takes place in three stages depending on how critical the situation is.
The stabilization system works very closely together with the dynamic steering, the damper control system and the sport differential. Audi has networked the chassis control systems of the new A8 in an innovative manner so that they now work faster and more closely together than before, with the ESP controller serving as the central integration platform.
The new A8 comes standard with a tire pressure indicator that is also integrated into the ESP. This is a system that measures indirectly, has no sensors of its own and thus adds no weight and requires no maintenance. It displays a warning on the onboard monitor to inform the driver of a loss of pressure in one or more tires. If only one tire is affected, the position of the tire is indicated. A warning is also given in the event of diffusion pressure losses, which lead to increased rolling resistance and thus higher fuel consumption.
This is possible because the tire pressure monitor not only compares the speeds of the four wheels as measured by the ABS sensors, it also monitors changes in tire vibration caused by stimuli from the road. In the event of a loss of pressure, the amplitude and eigen frequency of the tire changes significantly, from which a change in pressure can be deduced.
Elegant and sporty: the wheels
The wheel program accentuates the sporty character of the new Audi A8, with sizes ranging from 17 to 21 inches. Advancements in the carcass and running surface of all tires provide for great comfort and low rolling resistance.
The 3.0 TDI and the 4.21 FSI come standard with six-arm, forged alloy wheels shod with 235/60 R17 tires. Audi equips the 4.2 TDI with cast wheels and 235/55 R18 tires. The standard sizes are also available in a winter version suitable for use with snow chains.
The selection of optional wheels is even more attractive. Audi offers 19-inch cast wheels in 5-arm and 10-spoke and 15-spoke designs shod with 235/50 or 255/45 tires.
The top of the line are two 20-inch wheels shod with 265/40 tires. Both wheels have ten spokes, but different designs. The forged wheels with machine-polished design surfaces are adorned with contrasting paint in Brilliant Silver. The cast wheels offered on the American market are attractively chromed. The chrome coating is applied using novel cladding technology that reduces the weight of each wheel by 1.2 kilograms (2.65 lb).
Anyone looking for the ultimate in dynamic performance will find it at quattro GmbH, which offers 21-inch wheels. Audi delivers the 9 J x 19 wheels with 255/45 run-flat tires upon request. Rubber elements in their interior allow them to be driven for at least 80 kilometers (49.71 miles) at not more than 80 km/h (49.71 mph) in the event of a loss of pressure. The Audi A8 has a tire mobility set on board at no extra charge, and a 19-inch or 20-inch emergency tire is available as an alternative. With the large tires, a full-size spare tire will be provided in the trunk upon request, but this reduces its volume by approximately 45 liters (1.59 cu ft).
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.