Audi S8 with new chassis

Achim hartmann
Audi S8 with new chassis
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D he main difference between driving a car and motorcycling? In purely transverse dynamics, it is this: The driver pushes the motorcycle to the inside in curves while the car leans out. Unless it's the new Audi S8 as in the picture above - it can put its body in, even as standard. To do this, it uses spring struts to press the wheels on the outside of the curve more firmly onto the road, thus lifting the body.

By counteracting the centripetal force, the body mimics the behavior of a motorcycle in a leaning position. It feels as spectacular as it reads: you turn the S8 into a left-hand bend, it compresses with the two wheels on the driver's side and rebounds with the opposite. As a result, the upper body and head tilt slightly inwards. It doesn't push him to the outside of the curve as it normally would. Wrong emotional world.

Camera scans the street

Achim hartmann
Thanks to the active chassis, the Audi S8 not only pulls individual wheels against bumps at; it can also lean into the curve - similar to a motorcycle.

The sensory misalignment is the result of a trick performed by the so-called predictive active suspension in Comfort plus mode. The Mercedes launched a similar form in 2014 in the S-Class Coupé - as an extension of the steel suspension including Active Body Control.

In the luxury Audi, on the other hand, the magic suspension is based on the standard air suspension. In principle, A8 customers can order it as an upgrade that costs € 5,450, only the S8 is basically on board. We explain how the innovation works under the technical descriptionthe following double page.

Incidentally, putting yourself into the curve only describes the photogenic part of being able to; the other relates to suspension comfort, but is no less spectacular: a camera scans the road for unevenness and sends it to a computer. It then instructs the adjusting elements in the chassis to raise or lower the suspension struts at exactly the right moment in order to level the bump in the ground - in the best case, the S8 compensates for them beyond recognition.

The current S- Great already, but because it will be replaced at the end of the year, Mercedes unfortunately did not want to provide us with an opponent for a comparison with the S8. So we travel in the Audi to the Bosch test center near Boxberg without competitors, to take the rough roads there as a reference under the big wheels.

The route there leads via the A 81. Here, the chosen one is already chosen good suspension comfort of the five-meter sedan. For the first time in its now 26-year career, the top Audi really reaches the level of the luxury class when it comes to soft springs. It is remarkable how fluffy it reacts to unevenness without the body swinging on long bumps.

This is particularly impressive when you see the vehicle in front of you how the body fits into the bump and then flips out while driving the S8 barely moves over it. It is all the more astonishing that the active suspension cannot show its capabilities on the autobahn: the wheels can only be raised and lowered up to around 30 km /h; at higher speeds, the system can no longer keep up with the computing power. Then the single-chamber air suspension works without camera support.

A new level of comfort

Achim hartmann
Even level crossings are largely consumed by the suspension in their depths. You can almost only hear them.

In principle, it has to be bright enough for the camera mounted above the rearview mirror to recognize contrasts; The computer uses the differences in brightness to calculate the task at hand. Regular bumps or elevations with a length of up to 80 centimeters, which the system does at least ten meters in advance, are optimally balancedmust detect. This requires good visibility, fog would be counterproductive.

Today, optimal test conditions prevail in the Boxberg test center. Various challenges for the suspension were simulated here over nine tracks. For example Belgian pavement, the so-called Grauwacke - deliberately laid so loosely that a conventional steel chassis raises the white flag with little more than walking speed.

The S8 rolls over it as if it were any village street . At a pace at which other test cars rock up so much that the body touches down, the Audi still signals room for improvement. Only the protruding pointed stones rumble into the carcass of the 21-inch wheels.

Entry like an SUV

Achim hartmann
The photo montage at the bottom right illustrates how the body buckles up by five centimeters when the door is opened. This makes getting in and out easier.

The limousine rolls over the cobblestones with similar ease and rattles along the washboard. Here, too, you can hear the nasty upheavals more than you actually feel them. This is an extraordinary performance that raises perceptible comfort to a new level.

Another trick is making the S8 pleasant to use - every time you open the door, the body rises by 50 millimeters (see photo below right). Access is thus about as easy as an SUV. So if you simply want to get in and out higher, you will now find a much more individual alternative in the luxury Audi.

If the sensors of the A8 detects an impending crash, the affected side even cushions about 80 millimeters; the other party involved in the accident hits the stable rocker panel, which can then optimally absorb the impact energy.

Hopefully this momentous scenario will remain theory; Instead, we focus on the transverse dynamic experiences on country roads. As described above, the S8 leans up to three degrees into the curve in Comfort plus driving mode. And that requires a new steering behavior, withthat you have to come to terms with first. Because leaning into the curve deceives the learned feeling for the limit area.

The approach to it usually announces the steadily increasing sway. So don't succumb to the mistaken belief that the S8 can punch any speed into the apex. Otherwise an alarming tire squeal just before slipping will tear you out of your dream world.

The fact that you have to get used to these peculiarities is actually the biggest disadvantage of the S8. Because in the luxury class you are used to that explains the car to the driver himself with inconspicuous servility and does not have to be explored first. Audi is taking a path that is atypical for its class.

However, the tilt function is only active in Comfort plus; on Auto and Dynamic it is used to compensate for roll. In conjunction with the standard rear-axle steering, the S8 achieves surprisingly high cornering speeds. During the slalom on the test track, for example, the five-meter ship stays as close to the pylons as normally only sports cars can. You have to get used to that too.

You should warm yourself up

Achim hartmann
In left turns the S8 rebounds to the right and thus braces itself against the Centripetal force.

The proud new car owner should first get used to the excellent self-steering behavior. The S8 oversteers, especially in fast corners (please do not confuse it with drifting): It turns in further than the steering movement would suggest.

Action and reaction are not in a linear relationship to one another, but appear exponentially . You have to open the steering slightly so that the Audi does not deviate in the direction of the ditch or oncoming traffic. Incidentally, this impression is reinforced by the dynamic steering with its variable ratio. It takes time for your own wealth of experience to be recalibrated.

So make it easy like the motorcyclists in spring: take a weekend with the S8 and warm up.

The S8 actively raises and lowers its chassis

Achim hartmann
The signal box (colored red) is sitting instead of the stabilizer between the struts. The ends open into the two reversing levers next to the round containers with the electric motors. The torsion bars are similar to stabilizers.

Electromechanical actuators can be used with the active chassis (standard on the S8, 5,450 euros extra for the other A8 models) Raise and lower the wheels individually. The command for this is given by a computer which is fed with data from the front camera. If it detects an unevenness, the actuators initiate that the suspension struts first move the body upwards in order to retract the wheels again in a defined manner at the level of the unevenness - and thus compensate for the bump as far as possible. The power is provided by an electric motor that sits in a large can. Its moment is translated by a gear unit with 1: 200 and passed on to a torsion bar. This acts on a lever as a deflection to the spring strut, which starts where the stabilizer actually exerts its force. Sounds complex? It is


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