Wheels and tyre pressure monitoring system

The 3.7-litre and 4.2-litre versions of the A8 have the elegantly sporty 10-hole 8Jx17" alloy wheels as standard, with size 235/55 R17 tyres. This combination blends excellent handling and comfort properties, and sets new standards of wet adhesion and rolling resistance.

The wheels range includes other wheel versions of sizes up to 8.5Jx19", with 255/50 R19 tyres. These produce even better dynamic stability, coupled with a quality of tyre comfort that befits the luxury class.

The new A8 is equipped with the tyre mobility system as standard, comprising an electric compressor and sealant. If the car suffers a puncture, this system enables the driver to reach the nearest service station without needing to change the wheel. The A8 can also be supplied with a full-size spare wheel as a no-cost option.

A permanent tyre pressure monitoring system is also available as an option for the new Audi A8. The system monitors the tyre pressure and temperature of each individual wheel. It informs the driver optically and acoustically via the display in the instrument cluster if there is a loss of pressure and indicates which wheel is affected. A summary of all the momentary inflation pressures and temperatures of all four wheels can in addition be called up via the MMI terminal. Correct values appear in green lettering, red values indicate that the pressure should be corrected without delay.

As an option: PAX wheels

This is the first luxury-class vehicle to be available with cast aluminium wheels with run-flat properties, the so-called PAX system. Its design means that the driver can continue for up to 200 kilometres at a maximum speed of 80 km/h even if a tyre is fully deflated. At the same time the PAX wheel guarantees a perfect synthesis of agility and ride comfort and therefore rounds off the A8's typical dynamic performance in perfect style.

Thanks to the run-flat properties of the PAX wheel, the driver can, in the event of a puncture, reach an Audi workshop of his choice instead of having to change the wheel himself or call a breakdown recovery service: a new dimension to mobility that befits the luxury segment.

The flat tyre still offers a high level of residual ride comfort - the driver does not perceive a loss of pressure as a permanent deterioration of running characteristics. However, to make the driver aware of an impending flat tyre or a gradual loss of pressure, the PAX system is only offered in combination with the automatic tyre pressure monitoring system. This means that the driver is kept informed of the condition of all wheels and is in addition reminded of the maximum permitted speed of 80 km/h if one of the tyres suffers a puncture.

The PAX system consists of a special wheel rim, a suitable modified tyre design and the actual emergency-run element, a support ring that sits almost in the middle of the rim and encloses it. On a conventional wheel/tyre system, the tyre bead is clamped behind the rim flange. On the PAX system the tyre is inserted into the seat of the rim flange. To make sure that the tyre remains safely in position, a lever action presses the tyre more firmly into its seat if subjected to loads - when cornering for example.

The size designation differs from conventional wheels: the wheel used on the A8 has the metric designation "500" which, in purely mathematical terms, is equivalent to a size 18.3 inch wheel. The tyre designation is 245/690 R 500 Y.

MMI operating concept: maintaining diversity, reducing complexity

With the integrated user interface MMI, Audi is providing an infotainment platform and a user concept for the new A8 that keeps operation simple through stringent logic. MMI in the first instance comprises the control panel (MMI terminal) in the centre console with a control button that can be turned and pressed and four control keys grouped around it.

On either side of the terminal - apart from the Return key for exiting the menu level - there are a total of eight function keys with which the user can call up the principal main menus directly. The second central component of the MMI, a 7?inch colour monitor, is positioned above the centre console in the dashboard and therefore at an optimum angle of view for the driver.

The highlight: the basic geometry of the monitor display corresponds in detail to the layout of the control keys and button in the MMI terminal. In other words, the driver uses the top left control key to select the function displayed in the top left corner of the screen. There is thus an intuitive link between visual perception and hand movements.

Easy learning process

The driver only needs to remember four basic rules for operating the MMI:

  • The main functions of the system - entertainment, communication, information and control of vehicle systems - are accessed by the eight permanently assigned function keys.
  • Within these function menus, the driver activates the required functions by turning/pressing the control button.
  • The control keys, to which different functions are assigned for each menu, provide access to further functions in the menu. These can be read off in the corners of the display which also vary depending on the menu selected.
  • The user simply presses the Return key to skip back to the next-higher menu level.

    The more frequently a function is used in the car, the higher up the menu structure it is placed, thus making it quicker and easier to access.

    The electronics architecture

    The field of electronics has long since advanced into automotive technology. This applies in particular to the luxury segment where driver expectations regarding communication, comfort and convenience systems naturally play a very important role.

    The new A8 therefore offers numerous innovative technologies in this area, some of which are available for the very first time in an Audi. These include, to name just a few examples, the advanced key access and authorisation system, one-touch memory personalisation and the radar-assisted distance control system known as adaptive cruise control.

    However, the Audi development engineers have by no means integrated innovations into the vehicle at a functional level only. Numerous new elements have also been introduced behind the scenes, in the vehicle's electrical system. In view of a dramatic increase in the range of functions available, it was also important to guarantee operational reliability and efficient energy management.

    Networking played a decisive role here. Five main bus systems connect all electronic components on board the new A8. The entire driveline - including engine, transmission and brake control units - is networked via a high-speed CAN bus. The infotainment components such as MMI, sound and navigation systems communicate via a further high-speed bus based on MOST technology. The comfort and convenience components, from door controls to air conditioning, are also networked with each other.

    An independent "gateway" control unit acts as an interface between the bus systems. This connects the drive, comfort/convenience and infotainment networks hence making a control centre like the MMI possible in the first place.

    The Audi development engineers also relied on new technologies for the vehicle's wiring systems. New bus systems - such as the optical MOST technology - have been used; these include plastic-based optical fibres and foil wiring which is particularly space-efficient.

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