The aluminum body of the new Audi S8 is strong, sturdy and amazingly light. Its weight of just 231 kilograms (509.27 lb) is a key reason for the sport sedan’s dynamics and efficiency. Including the standard quattro drive, the S8 has a curb weight of just 1,975 kilograms (4,354.13 lb).
The body in Audi Space Frame (ASF) technology is roughly 40 percent lighter than a comparable steel body. Its layout follows bionic principles. The skeleton comprises extruded sections and pressure diecast parts of aluminum; the aluminum panels are joined to it using friction connections. Like the bones in a skeleton, all of the components combine optimal function with low weight. The material is used only where necessary and always in a tailored configuration.
The most recent stage in the evolution of the ASF principle is composite construction with steel to further improve crash safety. The B-pillars of the S8 are made of hot-shaped steel. The blanks are heated in a pass-through furnace to roughly 900 degrees Celsius (1,652 degrees Fahrenheit) and fed into the press directly thereafter. The blank is then quenched to approximately 200 degrees Celsius (392 degrees Fahrenheit) in the cooled die, creating a structure with extremely high tensile strength. This measures 1,500 Newtons per square millimeter in the upper section of the pillars; somewhat lower in the lower section because this is where most of the energy is dissipated in the event of a side impact collision.
The hot-shaped B-pillars make up eight percent of the weight of the S8 body’s material matrix, with most of the rest being aluminum – 35 percent panels, 35 percent cast components and 22 percent extruded sections. Joining these wrought components and individual parts is a high-tech process. Audi uses a wide variety of joining techniques – punch riveting, self-tapping screws, spot welding, MIG welding, laser welding and combined bonding.
Laser welding is an Audi domain. Because the seams exhibit high strength and rigidity, it can be used to join large panels to the structure. One area where laser welding is used is the aluminum invisible seam between the roof and the side of the car.
This is an area at the focus of all of Audi’s precision during the design and body assembly processes – the maximum tolerance for the outer skin is only 0.1 millimeters (0.004 in).
The ASF body is not only lightweight, it is also very rigid. Its static torsional stiffness has increased by 25 percent versus the predecessor, which was already a leader in the field. Dynamic torsional rigidity has improved by 15 percent, and lightweight quality – the relationship between weight, torsional stiffness and size – by 20 percent.
The ASF principle ensures comfortably low levels of vibrations and a tranquil interior free of disturbing vibrations or noises. The windows of the S8 also contribute to comfort, with double/acoustic glazing standard. Audi also offers infrared-insulating and heated windshields as options; dark privacy glazing for the rear windows is another option.
Highly tuned: the aerodynamics
The S8 glides smoothly through the wind. It has a drag coefficient of only 0.28, with the frontal area measuring 2.41 m2 (25.94 sq ft). Low lift coefficients at the front and rear axles ensure outstanding stability at highway speeds. The almost fully lined underbody and the low-loss flow of air through the engine compartment were also high on the list of the aerodynamic engineers.
The ASF body of the S8 offers extremely good protection in the event of a collision. In a frontal collision, four load paths distribute the forces optimally to each side of the vehicle. A cross-member manufactured out of a double-box section and bent into the shape of an omega provides additional protection for the passenger cell. The longitudinal members in the floor panel come together in the shape of an arrow below the rear bench seat. Together with the center tunnel they constitute the body’s strongest node. The longitudinal members in the rear are large.
Standing guard in the large sedan’s cabin is the adaptive restraint system. It is networked with the Audi pre sense safety system and draws its own information from eight sensors. It intelligently manages the interplay between the airbags and the belt force limiters to offer outstanding protection to passengers of any size. In a rear-end crash, the integral head restraint system works together with the seat backs to avert the danger of whiplash injuries.
All Audi models are equipped with four side airbags to support the hips and chest of the occupants in the event of a side-impact collision. The head airbag system spans the area from the A-pillar to the C-pillar and opens like a curtain. All of the seats in the new Audi S8 have three-point automatic seatbelts with tension limiters. Isofix child seat anchors in the rear are standard. A deactivation function for the passenger-side airbag is available for an extra charge.
To help hold down the cost of repairs, the aluminum crash boxes bolted in front of the cross-members at both the front and at the rear of the car are relatively easy to replace.
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.