With a car this big the weight advantage of an aluminium shell is soon forgotten!

Not to be outdone by Mercedes' new S600, Audi have just released details of the new A8 4.2 Quattro with an extra-long wheelbase, to cater for those who do not drive their own cars. With an overall length of 5.2mm, 130mm more than the standard car, the new Audi A8 long-wheelbase provides rear seat passengers with an impressive 70mm of extra legroom. The extra length has been added between the B and D pillars, and as a result the rear doors have been extended by 130mm, making access to and from the back seat even easier than before. Compared to the standard Audi A8, the long-wheelbase version also offers additional headroom in the rear seat area. To achieve this, the seat has been moved forward by 60mm in relation to the rear axle. Elbow and shoulder room have also been increased.

The Audi A8 long-wheelbase will initially be available with the 4.2-litre V8 engine which provides 310bhp and 302lb.ft of torque. This unit, modified last year to incorporate Audi's sophisticated five-valve technology, is allied as standard to a five-speed Tiptronic transmission and Quattro permanent four-wheel drive. Why go to all that effort if your chauffeur is going to do all the driving?!

The car's specification is expected to closely match the standard A8 4.2 Quattro, with principal features including 'Competition' alloy wheels, remote control central locking (radio wave), an electric sunroof, electrically adjustable seats upholstered in Nappa leather, polished burr walnut trim, cruise control and an audio system with six CD autochanger.

The list of safety and security features is equally extensive, and includes an alarm and transponder immobiliser, pyrotechnic seatbelt pre-tensioners, ABS with Electronic Brake Force Distribution, Electronic Differential Lock and Anti-Slip Regulation traction control and Audi's Electronic Stability Program. That's ABS, EBFD, EDL, ASR and ESP in case anybody is interested!

Eight airbags are also fitted as standard to maximise accident protection. In addition to the two full-size front airbags and the four side airbags integrated into the seat backs, the new generation Audi A8s have two additional 'sideguard' airbags mounted in the roof lining. When triggered the new system covers virtually the entire side window area in the event of a side impact.

Prices and full specification for UK versions of the new Audi A8 long-wheelbase have yet to be finalised, and will be announced nearer launch towards the end of 1999.

Electronic tyre-pressure monitoring system
Accompanying the new long wheelbase version of the A8 is a new technology for Audi drivers - electronic tyre-pressure monitoring. The performance potential and operating safety of a tyre depends to a major extent on its pressure. Too low a tyre pressure has a negative effect on rolling resistance, fuel consumption and tyre wear. In order to ensure that the correct tyre pressure is present at all times, it is necessary to check it regularly, but in practice this task is performed very rarely, if at all - especially not by owners of luxury vehicles.

An electronic tyre-pressure monitoring system will be available for the Audi A8 and S8 Quattro models from September 1999 as an optional extra to improve safety and reduce the need for routine maintenance. Plans are currently in hand to make the system available on other Audi models in future.

The new technology eradicates the need to remove and replace valve caps and connect and disconnect hoses or air pumps when checking the tyre pressures. A particularly important function of the tyre-pressure monitoring system is to inform the car's occupants of any potentially dangerous situation that may have arisen because of a pressure loss in the tyre caused by, for example, driving over a sharp object which might otherwise not be noticed until it is too late.

The tyre pressure is constantly checked by the monitoring system, whether the car is at a standstill or in motion. The driver is informed of any significant pressure drops in one or more of the tyres via a central display on the dashboard, with two priority levels. Level 1 applies to tyre pressure drops of more than 0.2 bar and has a yellow symbol, advising the driver to correct the pressure at the next available opportunity. Level 2 registers drops of 0.4 bar or rapid tyre-pressure drops by displaying a red symbol meaning: "imminent danger, stop immediately".

If only one tyre is affected, its position is displayed, for example "Tyre pressure, rear left". The system thus records both the normal, very gradual tyre-pressure reduction caused through air diffusion losses and also slow or rapid drops in pressure caused by damage to the tyres. The Audi system memorises the tyre pressures once they have been correctly adjusted by the driver. Because the tyre pressure at any given time is temperature-dependent, the reading is adjusted by a temperature compensation factor. Clever stuff. When new tyres are fitted, the monitoring system takes the new tyre pressures into account during the first journey.

The tyre-pressure monitoring system consists of battery-operated wheel electronics, mounted on the valve inside the tyre. A sensor measures the tyre's pressure and temperature. These values together with additional data are then transmitted with the individual wheel code as a data telegram. The radio aerials integrated into the wheel arches are not visible from the outside; they receive and transmit the data telegrams and forward them via screened twisted-pair cables to the control unit. This evaluates the data telegram, identifies the tyre from which the information comes and assigns it a priority level.

Intelligent energy management ensures that the Audi system operates reliably and with only minimum current consumption. The tyre pressure is measured every three seconds but, unless something is seriously amiss, only transmitted to the control unit every 54 seconds. The driver only receives messages if tyre pressure problems arise. If the measured values start to drop by 0.2 bar per minute, however, the system shifts to a faster transmission mode: it then takes a reading every 0.8 seconds. The driver is advised to stop the car in good time and can bring it safely to a standstill. When the Audi A8 is parked, the control unit goes into the sleep mode to prevent the car battery's service life from being compromised.

The tyre-pressure monitoring system operates at temperatures ranging from minus 40 to plus 120 degrees Celsius. Dynamic peak values of up to 2,000 x gravitational acceleration and speed (where permissible) of more than 300kph (186 mph) do not affect its function. I bet some German drivers will try to challenge that!

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