A 6 steps up aclass; Theirs is new air luxury about Audi, s big saloon - espcially if you invest the upgraded suspension system writes RUSSELL BRAY.

Byline: RUSSELL BRAY

I USED to think that Audi's big A6 saloon, though excellent in terms of build quality and cabin ambience, was overshadowed by its even bigger brother, the A8.

But midway through 2004, Audi launched the all-new A6 which, thanks to niftier styling and that dominant, single-frame front grille, has considerably more on-street presence.

And now that the car is available with the absorbent adaptive air suspension system as used on the luxurious A8 - albeit at an pounds 1500 premium - it has a much stronger position in the market place.

With different settings and levels of suspension damping available on demand via the multi-media interface (MMI) control system, the A6 feels much more like a smaller A8.

It's able to change from a superb long-distance cruiser to a sporty saloon at a press and twirl of the knurled dial.

The driver whose A6 is fitted with adaptive suspension can consistently choose a setting for all road conditions and to suit their individual style of driving.

The only downside is that the MMI system, while not as tricky to operate as BMW's i-Drive, is still too complex and you'll need self-control or it will distract your attention from the road.

Despite being much-improved, the new A6 remains one of the most affordable executive saloons. Prices start at just over pounds 25,000 for the two-litre FSI turbo petrol or the two-litre TDI.

The flagship model is the pounds 45,900 4.2-litre quattro S line, but it was one of the diesels I was keenest to try.

In line with their reputation for advanced engineering, Audi are building an increasing number of diesel engines with high-tech piezo injection.

These injectors allow up to five separate amounts of fuel to be injected on each working stroke of the engine, which is incredible considering the small timescale involved.

And the result is smoother engines that deliver improved fuel consumption while making less noise.

I test drove the pounds 31,385 3.0 TDI quattro, but with automatic transmission (pounds 1400 extra) and air suspension.

Acceleration to 62mph takes a fraction over seven seconds, which is rapid for a car of this size, especially considering the extra energy needed to keep all four wheels powered all the time.

It helps that the six-speed Tiptronic automatic transmission is 14kg lighter than the old five-speeder, and that the overall range of gear increments is up by 18 per cent for better acceleration at low speeds and lower revs at high speed.

Top speed is more than double the UK motorway limit, yet you can expect fuel returns of around 33mpg overall and 23mpg when driving in town.

In my experience Audis have never felt anything but solid, but the new A6 has a body that is 34 per cent stiffer than the previous model, which helps improve ride comfort and precision of handling.

Longer and wider, it also has much improved front shoulder room. There's masses of rear legroom, too, as the rear wheels have been pushed further back.

At 546 litres, the A6's boot is larger than those of all its rivals.

Standard equipment across the range includes cruise control, digital comfort air conditioning, a CD player and automatic headlights and wipers.

The tempting options list includes features such as tyre pressure monitoring, adaptive xenon lights and radar-assisted cruise control.

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PERFECTLY EXECUTED: Cabin ambience remains a strong point of the Audi A6' Audi A6