Quattro has been an integral part of Audi’s development from a bit-part player to a global sales phenomenon. The brand now offers 4WD on every car it sells.
But while the quattro badge remains the same, different models have different types of four-wheel drive. However, the latest A6 Allroad uses a transmission that can trace its ancestry back to the successful Quattro rally cars of the early eighties. Over the years, it’s evolved to deliver serious performance in all road conditions. And the raised ride height means the A6 Allroad is also capable of taking on the occasional bit of light off-roading.
Like the Subaru XV, the Audi has permanent all-wheel drive, but it uses a Torsen (TORque SENsing) differential, which splits the power 40:60 between the front and rear wheels. This is intended to make the A6 feel like a sporty rear-wheel-drive model on the road, but in challenging conditions, up to 80 per cent of the 3.0 TDI diesel engine’s power can be sent to the back wheels when required.
The advantage of a Torsen mechanical differential over an electronic system is that it diverts the power instantly. So rather than reacting to road conditions, it’s constantly shifting drive to the axle with more grip at any given moment. This system was first introduced on the Audi RS4 in 2007 and has since been used by all the larger models in the range, from the A4 to the big Q7 SUV.
Yet while the set-up works very well on the road, the earlier quattro-equipped cars could easily get stuck, as the diff didn’t always send power to the other wheels if one of them lost grip entirely. To counteract this problem, early cars had a locking rear diff, but modern Audis – such as this A6 – feature a clever electronic differential lock (EDL). This uses the brakes and ABS sensors to limit wheelspin and make sure plenty of power is supplied at all times.
At speeds below 50mph, EDL is constantly turned on to ensure the Allroad doesn’t get stuck. The beauty of this system is that you rarely notice it’s working: at the track, the A6 had lots of grip and remained totally stable, even during committed cornering at high speed. The system also worked in tandem with the car’s seven-speed S tronic box to post a rapid 0-60mph time of 5.9 seconds.
But when you take the A6 off-road, it’s a bit less successful. The standard Drive Select button has an Allroad setting that raises the air-suspension and relaxes the car’s throttle response and steering to suit trickier driving conditions. There’s also a hill-descent control feature that displays your current tilt angle.
Yet despite these sophisticated electronics, the wide cross-section road tyres struggled in the mud. And not all buyers will want to risk heading off-road in such an expensive estate car – our test model was £65,515.
Still, the Audi has few equals as a capable all-weather road performer, and we think the quattro drivetrain deserves its reputation.