To celebrate in style, Audi has unveiled two models to mark this milestone. Later in the year, it will launch the successor to the much-loved RS2 Avant, the twin-turbo 2.7-litre V6-powered 380bhp A4-based RS4 Avant. Available much earlier, though, is this - the A6 Allroad quattro.
Based on the A6 Avant, Audi's first foray into the off-road sector brings with it a host of cosmetic, suspension and engine changes that the company claims elevates it above and beyond the more traditional four-wheel-drive offerings.
Against such stalwarts as the Mercedes-Benz M-class, Land Rover Discovery, Jeep Cherokee and Toyota Landcruiser, the A6 Allroad quattro does without the vertiginous seating position and dubious on-road driving dynamics but packs the off-road capabilities of a mountain goat.
From the outside, the wide track and taller body height combined with flared wheelarches, pronounced bumper mouldings and twin chromed tailpipes differentiate this A6 from its 'lesser' compatriots. But it's underneath where the real differences take place. To give it the same ground clearance as other mud-pluggers, Audi's answer is four-level air suspension that varies the height in relation to road speed. Add in a Torsen self-locking centre differential which can divert two-thirds of the engine's power to individual axles to reduce wheelspin and increasing its all-terrain attack is an Electronic Differential Lock (EDL) that can keep the Allroad moving even when only one wheel has traction.
Power comes from two familiar V6 powerplants tweaked to provide extra torque at low speeds and matched to either a six-speed manual transmission or a five-speed automatic with a self-shifting manual override. With a high-pressure injection pump and a turbocharger, power from the 2.5-litre V6 TDI is up to 180bhp with peak torque rising by 20% to 273lb-ft. For petrolheads, there's the twin-turbo, 30-valve 2.7-litre V6 engine from the S4 and A6 quattro models with 250bhp and 229lb-ft of torque.
Performance statistics are equally impressive with the 2.7T recording a 0-62mph time of 7.4secs and a top speed of 147mph. The V6 TDI is no slouch, however, recording 9.5secs and 129mph respectively. Average fuel consumption is 22mpg for the 2.7T and 31mpg for the V6 TDI.
On the rough stuff, there were few climbs during our test drive that beat the Allroad. Admittedly, the 'off-road' course was more of a challenging green lane than a quagmire - although none of the test cars had the £1,000 optional low-ratio transmission fitted, grip and traction was immense. Even on steep inclines lined with wet grass, any loss in traction simply provoked the EDL into action by braking the spinning wheels and transferring power to the one with most grip. At first it's unnerving because the car actually stops before forward motion returns. The TDI's extra torque is useful off-road, although watch the revs because at very slow speeds you can quickly find yourself off-boost and struggling for power.
But it's on-the-road where the Allroad trounces the opposition because there's very little difference between it and any A6 quattro. Even with the suspension set in its highest position, the ride is relaxed and smooth without a hint of the floating sensation often generated in 4x4s, but with the ability to lower the height at will, it is a fast and supremely refined luxury estate car. After testing the 2.7T quattro earlier this year, we commented on the improvements made to the steering without the over-assisted feel akin to most Audis we've driven and the Allroad is no different - for such a big car the Allroad is amazingly agile.
Inside, bar a set of aluminium-rimmed instrument dials, colour-coded trim and supportive seats, the Allroad is pure A6, which means first-class build quality, excellent ergonomics and ample space up front.
Standard equipment includes twin and side airbags, ISOFIX child seat mountings, traction control, Electronic Stability Programme, alloy wheels, larger door mirrors, cruise control, electrically-operated seats, ABS with EBD, climate control and front and rear undertray protection. There's even a set of unique tyres, aptly named Allroad, designed for on-road/off-road use.
On the road prices start at £32,550 for the V6 TDI and £36,630 for the 2.7T. With no 4x4 5-series available, BMW's closest rival is the BMW X5 which is due on sale in September: it might be as capable off-road but with a top speed of 129mph it's not as fast nor can it match the Allroad's price - the X5 is estimated to cost about £46,000. Likewise Mercedes-Benz's ML320. At £32,390 it undercuts the Allroad by over £4,000 but with a top speed of just 113mph and a 0-62mph time of 10.1 seconds it's much slower.
When the benefit-in-kind tax laws change in 2002, at 307g/km the Allroad 2.7 undercuts the ML320 by 23g/km and the X5 by 28g/km. For a 22% taxpayer, the bill will be based on the maximum 35% of list price, giving an annual figure of £2,820. Drive the ML320 and you'll pay £2,494 and an estimated £3,542 for the X5.
Bearing in mind most off-roaders never go off-road, it makes sense to buy one that doesn't sacrifice on-road performance. The A6 Allroad fits the bill precisely.