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Whereas BMW’s xDrive systems relies almost entirely on electronic processing to work effectively as a true all-wheel drive solution, Audi’s Torsen equipped Quattro system does not. It is a purely mechanical system designed, not for off-road use – though it copes admirably with all types of road and track surfaces – but for a dynamic and infinitely variable on road driving experience through the use of the widely lauded torque sensing centre differential. BMW does not make use of a traditional, open centre differential to distribute power and torque front to rear in the same way that, say, Audi or Subaru do by virtue of a regular differential coupled with a limited slip device. So, BMW’s system relies wholly on electronics to even out the differences in axle wheel speed front to rear when cornering. It’s a drivetrain that doesn’t lend itself to abuse either in the way that Quattro or Symmetrical All-wheel Drive do. Standard launch procedures in an A4 quattro? Get the revs up to 5000 rpm and sidestep the clutch. Somehow that drivetrain manages to take all of that punishment without disintegrating into a thousand pieces. It’s a seldom published fact that BMW’s system doesn’t cope as well with such brutal treatment.

So, BMW have gone the route of an electronics-centric all-wheel drive solution and Audi have gone the mechanical route. Note, the AWD system in the Audi is in no way connected with the ESP system. ESP operates over and above the Quattro drivetrain as it would in any two-wheel drive Audi. It does not interfere with the operation of the Torsen differential directly. Now which one is better? It would be remiss of me to disregard the capability of xDrive based solely on its reliance on electronics. Let’s face it: modern electronics make cars work far far better than they ever did. In the engine, at the brakes, in gearboxes, in drivetrains and so on, electronics have enabled astounding progress in the capability of modern automotive engineering. Look at today’s modern engine? Where the hell would we be without knock sensors and lambda sensors and electronic fuel injection and variable valve timing and electronic throttles and (phew!) and…? Nowhere. So, step in electronically enhanced all-wheel drive. Electronics allow for precise, micro time-frame calculations that measure a loss of traction long before the driver is remotely aware of the problem. In doing so, a driver input that may cause traction to be lost is softly and imperceptibly adjusted by xDrive and the DSC (or DTC or whatever they want to call it) in conjunction to produce a fully integrated system that is able to dynamically react to any loss of traction, make the required decision and affect the necessary action (at engine, differential and brake systems) in a fraction of a second. This is why the xDrive systems perform so well in truly icy conditions. It’s all down to complete electronic intervention.

That’s not to say that xDrive is superior. The mechanical systems of the Audi provide for some of the most seamless, intuitive and enjoyable AWD experiences, around free from the constant intervention of the nannying electronics. Let’s face it, electronic systems save the day but a purely mechanical interface between the driver and the road is still deemed as being the most rewarding because it’s the most communicative and involving no? This is where Quattro in cars like RS4 shines. It’s an all-wheel drive system that was designed from the get go to enhance the motoring experience behind the wheel; it’s mechanically pure and hence unencumbered in delivering that “connected” feeling. This argument, admittedly, can be considered as being circular because no one can deny that cars that employ extensive electronic aids in their all-wheel drive systems such as the EVOs and GT-Rs of this world are equally enthralling from a driver involvement perspective. There just isn’t a right or wrong answer here…

Ultimately it boils down to consumer preference, because no post, no matter how long will solve the debate around which system is superior for on-road use in both good and inclement conditions. And that leads me on to the next discussion…

End of post 2 – continues…