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 tire 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.
There are two warning stages: a pressure loss of more than 0.2 bar at a wheel triggers a yellow warning lamp. This tells the driver to check their tyre pressure and top up the air to the correct level at the next opportunity. If there is a pressure loss of more than 0.4 bar or in the event of a sudden loss of pressure, the warning appears in red: in this instance the driver should stop as soon as possible and rectify the situation.
A summary of all the momentary inflation pressures and temperatures of all four wheels can now also 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 a 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. This technology makes sure that the tyre remains on the rim even if it is completely deflated.
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 safety in position, a lever action presses the tyre more firmly into its seat if subjected to loads - when cornering for example.
The PAX wheel can be recognised by its original 7-arm design for which both summer and winter tyres are available. 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.
With high-performance brake system
The new Audi A8 is fitted with a newly developed high-performance brake system that is fully in keeping with the demands and the character of a sports saloon in the luxury segment. This applies both to deceleration potential as well as to stability and braking comfort.
The brake system on the eight-cylinder versions of the new A8 is much larger than on the predecessor model: aluminium floating-caliper brakes are fitted at the front and rear. With 360 millimetre brake discs at the front and 310 millimetre discs at the rear, the system now also achieves a braking performance in conjunction with 17-inch wheels that was previously reserved for 18-inch systems.
The brake system is supported by the Electronic Stabilisation Program ESP 5.7 with ABS, ASR traction control, Electronic Brake-force Distribution EBD, Electronic Differential Lock EDL and hydraulic brake assist.
Electromechanical parking brake
The electromechanical parking brake is also making its debut on the Audi A8. It brings clear functional benefits as well as performing all the tasks of a conventional handbrake.
The system, operated via a pull/push control on the centre console, automatically ensures the necessary parking brake application force. The operating concept is deliberately based on what most drivers would consider the usual operating principle for conventional systems: a quick pull of the switch applies the brake; if the driver pushes it down - while the brake pedal is depressed - the system is released.
The parking brake's status is indicated by tell-tale lights in the control element and in the instrument cluster.
The system is designed for gradients of up to 30 percent. If this is exceeded, the driver is warned by a text message ("vehicle too steep").
By way of an integral starting assist function, the electromechanical parking brake moreover makes it easier to pull away without jolts or rolling backwards on inclines, without the driver needing to release the brake by hand.
The system calculates the moment and rate at which the parking brake is to be released, on the basis of data such as the transmission position selected, the accelerator pedal position, the engine speed and the angle of inclination. As soon as there is sufficient torque to move the vehicle forwards, the electronics automatically release the parking brake.
It goes without saying that the electromechanical parking brake also has the emergency braking function stipulated by law: above a speed of 8 km/h the driver can stop the vehicle simply by pulling on the switch - if the foot brake system fails, for example. A deceleration rate of 8 m/s2 - which is significantly more than with a conventional handbrake - can then be reached in scarcely more than a second.
A brake-pad monitoring system, which informs the driver in the cockpit of the current status, is combined with the electromechanical parking brake.
There is a further advantage to the electromagnetic parking brake: by eliminating the conventional handbrake lever, it enables the designers to give the centre console a new, neat layout.
Engine and transmission: Light and powerful: V8 engines with five valves per cylinder
Even in the early years of car manufacture, eight-cylinder engines were a trademark of progressive technology at Audi. The Horch cars of the 1930s owe their legendary reputation not least to this outstanding engine technology.
In 1988 Audi began producing the modern generation of V8 petrol engines. Together with the Audi Space Frame ASF, the V8 engine formed the technical basis for Audi's breakthrough into the luxury car class.
When the new Audi A8 goes on sale in autumn 2002, there will be a 4.2-litre V8 version developing 246 kW (335 bhp) and a 3.7-litre counterpart with an output of 206 kW (280 bhp). This means an extra 25 bhp (4.2-litre) or 20 bhp (3.7-litre) compared with the same-sized engines in the previous A8.
The torque of these two engines also represents a clear advance on their predecessor versions: 430 (4.2) and 360 Nm (3.7) guarantee superlative acceleration and agile sprinting at all speeds.
The A8 4.2 quattro accelerates from 0 to 100 km/h in just 6.3 seconds; the 3.7 quattro needs only one second more. Both V8 engines are capable of a top (governed) speed of 250 km/h.
The gain in sports performance is also suitably reflected by the car's appearance: a glance under the bonnet reveals that these beefy engines have been given a new design. The intake manifold and injector rail, ignition coils and cylinder head covers are no longer hidden underneath a plastic cover: on the new Audi A8, the engine's technology and performance potential are quite literally there for all to see.
Camshaft adjustment and variable intake manifold
Both V8 alloy engines have a five-valve cylinder head with adjustable inlet camshafts and low-friction roller cam followers.
Both V8 engines have one variable camshaft system per bank of cylinders, to vary the valve timing of the inlet camshafts in various engine speed ranges. With the aid of the engine oil pressure, the free length of the timing chain between the inlet and exhaust camshafts is varied by an adjusting piston. This produces a twisting of the inlet camshaft relative to the crankshaft. The range of adjustment is a crank angle of 22 degrees on the 4.2-litre and 13 degrees on the 3.7-litre engine.
The variable camshaft system is controlled by a mapped characteristic and ensures good idle quality, low untreated emissions and an ample torque curve across the entire speed range.
The Audi engine specialists have redesigned the poly V-belt drive which operates a particularly efficient water-cooled alternator. An automatic belt tensioner ensures particularly low-vibration and low-noise running of the poly V-belt.
The 4.2-litre V8 in the new Audi A8 has a two-stage variable intake manifold that has already proved its worth in the S8. Intake manifold lengths of 705 and 285 mm enable ideal intake air resonances and consequently a torque and performance enhancing self-charging effect across a wide speed range.
The short-stroke 3.7-litre engine has a three-stage variable intake manifold that makes use of the required vibrations particular at low revs and therefore guarantees a powerful torque development across the entire speed range.
Lightweight construction using magnesium, aluminium and plastic components reduces engine weight to below 190 kg. Together with their compact outside dimensions - the engine is only 504 mm in length - both V8 units are in this way the ideal choice for the overall concept of the Audi A8.
Not least thanks to the systematic application of lightweight design, the new A8 generation moreover exemplifies a pioneering approach to fuel consumption, for all its dynamic potential. It manages on a very modest 11.7 litres (3.7) or 11.9 litres (4.2) of Super Plus per 100 km (overall fuel consumption according to 1999/100 EC ).
The emission values for both V8 engines are of course well below the limit figures of the EU IV standard. To this end, each bank of cylinders has a close-coupled two-stage catalytic converter which reaches its optimum operating temperature particularly rapidly, even after a cold start.
Fully integrated automatic starting
Fully integrated automatic starting is a new function for both V8 engines. If the engine control unit is authorised to start the engine by the driver authorisation system, it independently takes charge of energising the starter motor.
This means that the driver no longer needs to hold the ignition key turned during the starting process: it suffices to turn it briefly in the lock or, in conjunction with the "advanced key" authorisation system, to press the starter button.
The dual-branch exhaust system of the two V8 engines in the new Audi A8 is deliberately aimed at a discreet yet decidedly sporty sound that makes the vehicle characteristics a pleasure to listen to as well.
A total of five silencers and fine-tuned vibration decoupling in several areas also makes sure that this sound is never perceived as unpleasant.
New engine mounts with an additional insulating layer prevent structure-borne noise from being transferred to the body. The significantly reinforced engine-transmission unit guarantees drone-free interior noise across the entire engine-speed range. Idle behaviour has also been improved considerably; it is now vibration-free and can practically no longer be heard.
New 6-speed tiptronic
Another new feature at Audi is the new 6-speed tiptronic with Dynamic Shift Program DSP and additional Sport program. Thanks to the extra speed stage, the engine's output and torque are always unleashed with such precision that the conflicting requirements of spontaneous power flow, high performance and perfectly refined running are all achieved.
The additional sixth speed moreover means that the spread between the lowest and highest ratios has been increased by 30 percent - a vital requirement of greater dynamism on the one hand and optimum economy on the other.
The front-axle final drive and transfer case are both integrated into the housing of the new 6-speed automatic transmission. Unlike all predecessors, the output to the front wheels is located in front of the converter.
The hydraulic control unit, the solenoid valves and pressure regulator and the actual electronic control unit are linked directly together and accommodated in the transmission oil sump. This arrangement makes it possible to dispense with a large number of the cable connections otherwise necessary.
Manual and automatic gear changes
Those who prefer automatic gear-changes will greatly appreciate the outstanding benefits of the adaptive electronics. A version of the Dynamic Shift Program DSP specially developed for the 6-speed tiptronic avoids excessively frequent gear changes - despite an additional gear compared with the five-speed predecessor.
The advantages of this are especially noticeable in conjunction with a sporty style of driving. For example, if the selector lever is in the "S" position, the program prevents upshifts if the accelerator is released suddenly. If the lateral acceleration sensor of the ESP then detects that the vehicle is cornering, upshifts remain blocked until the end of the bend is reached. The system thus avoids the drawback familiar from many conventional automatic transmissions, namely of changing up going into a bend followed by a change down coming out of it again.
Gears can also be changed manually, using the selector lever in the tiptronic gate. As a new feature on the A8, drivers also have the option of changing gear using the shift paddles behind the steering wheel: an operating concept that has already proved successful on the triumphant Audi R8 Le Mans racing car. The driver can therefore change gear when cornering, without having to take his hands off the steering wheel.
quattro permanent four-wheel drive
The quattro four-wheel drive system which the A8 3.7 and 4.2 use to transfer engine power to the road remains an utterly unique feature in the luxury class. quattro maintains outstanding traction and lateral support, and minimises the effect of propulsive forces on the car's self-steering properties. This is a vital condition of tremendous cornering speeds and a high level of dynamic stability. In other words, maximum driving fun and active safety.
On the new Audi A8 - with its longitudinally installed engines - a Torsen differential automatically establishes the optimum distribution of power between all four wheels. The name "Torsen" is a contraction of the two terms "torque" and "sensing". The Torsen differential is a self-locking worm gear.
The advantage is that the locking action is only prompted by the driveline. This type of differential accommodates differences in speed when the brakes are applied and when cornering. Normally the power is split 50:50 between the two pairs of wheels, but in extreme cases 75 percent of propulsive power can be diverted to either pair. In the event of more than one wheel encountering considerable slip, the Electronic Differential Lock EDL can even concentrate this power on one wheel.