Testing the new Audi differential system on Canada's icy roads

Audi engineers came up with a complex new rear sport differential and centre crown gear system that all but cures the problem.

Listening to some boring engineers drone on for 60 minutes about all-wheel-drive is surely the cure for the sleepless night. Even the most incurable insomniacs can only take so many torque splits and slippage ratios before their eyes start that relentless droop downwards that the eternally restless crave. Throw in seemingly endless discussions on multi-plate friction clutches and a marketing guru who waxes lyrical about 3.7 million Quattro-equipped Audis already sold and you have a presentation that even the apparition of Pamela Anderson wielding a big pointer for the presentatioin can't cure.

A remedy, however, is not very far away. Indeed, one ride through the Quebec woods with Harald Demuth in his 1985 short-wheelbase rally racer is quite enough to keep one awake for a week. Yes, Formula One is faster and Nascar more lucrative, but there's nothing quite like jumping over a blind hill on the wrong side of 140kph through a deeply wooded goat path covered with ice so slippery you can't even walk on to get the old adrenaline gland pumping.

Even for we Canadians such antics are truly outrageous. Yes, we are the land of the mukluk and the igloo but most of us hate the cold as much as the rest of the world, and are just as scared of driving around on slick roads. So when Demuth was tossing the ancient Quattro into some seemingly out-of-control, full-lock slides with really big fir trees looming out my side window, I too was suddenly wishing that I really had paid more attention to the discussion of the superior tractive abilities of the 60/40 torque split.

It is the 30th anniversary of Audi's introduction of the famed Quattro, hence the presence of 1982 German rally champion Demuth and his 450hp Group B racer (as well as Frank Sprongl, Canada's all-time leading rally racer, and his even older long-wheelbase version). Like most such anniversaries, Quattro's 30th is being accompanied by a public relations campaign (in this case "Fascination") and a push of some newer all-wheel-drive technology that promises, as with all such product advances, to do nothing short of solving all of Audi's problems, perfect the automobile and possibly even cook the perfect eggs Benedict. Despite the caffeine-like jolt of my plummet through the woods with Demuth, my natural scepticism tells me this will be another minor advancement akin to all the other high-tech wizardry that engineers luxuriate upon automobiles these days - yes, I can feel the difference the adjustable suspension/revised veh -adjustable steering makes but only if I concentrate all my limited sensitivity into my seat-of-the-pants dynamometer.

Not so with Audi's new sport differential.

First, a little bit of background. Read any recent Audi road test (save the R8 coupe) and the results are pretty much the same; great car, fantastic interior, will never handle as well as a BMW because of the awkward weight distribution. You see, Audi, in its quest for superior interior space, places its engines as far forward as possible in the chassis, often ahead of the front axle. All that weight concentrated in the front of the car inevitably results in understeer, that feeling that the front wheels are slightly less enthusiastic about turning than the driver. Though it's hardly a limitation in a normal saloon driven by normal motorists on normal roads, it can be a severe limitation for Audi's sporting products. Even the best of them - the TT RS, S4, etc. - will push the front end, sometimes dramatically, when seriously hooning down twisty roads.

No more. While most critics thought the only solution would be for Audi to move its engines rearward, Audi's engineers were unwilling to compromise their interior packaging. Instead, they came up with a complex new rear sport differential and centre crown gear system that all but cures the problem. It's a complex system, with multiple clutch packs, twin "sun" gears, two more "crown" gears and a really nifty bi-functional hydraulic actuator that compresses multiple functions into an apparatus not much bigger than a cigarette package. It's an amazing system though I fear that any more complex discussion may need graphs and pie charts to get you through the complexities of torque-vectoring and differential speeds. All that you need to know about this last is that a) it essentially distributes more power to the outside rear wheel whenever the car is cornering and b) it really works well.

Beyond expectations, actually. Drive a conventional Audi round a very slippery 60-metre ice circle, for instance, and even the tiniest application of the throttle sees the front end-skidding towards the trees that suddenly feel too close for comfort. Flip the MMA computer control so that the sport differential is now in dynamic mode and, suddenly, the very same car is transformed; you can actually punch the throttle and have the big A7 hold its line tenaciously. Flip the traction control completely off and suddenly you're Demuth, able to hold the big Audi in long, lurid drifts as if you know what you're doing.

The difference is even more dramatic in the new ultra-sporty RS5. Normally, 450 horsepower and ice as slick as a hockey rink would not be a good mix. Indeed, in its conventional mode, I'm tiptoeing the big sports coupe through the icy race track Audi has set up in northern Quebec like Mariah Carey in full diva mode; don't touch the throttle and absolutely no jerky movements on the steering wheel.

Flip the system again into full dynamic mode and I can do no wrong. I power out of corners in one great-perfectly snow-spewing slide, the new Quattro system's various clutches and sensors determining exactly how much power to send to which wheel to maintain that perfect yaw angle. Even the most diabolical off-camber, uphill hairpin with minimal traction becomes a simple procedure of holding the steering wheel in a constant position and just mashing the throttle. I'm suddenly ready for World Rally Championship competition. Unlike most such technologies, Audi's new sport differential - available on Q7, S4, S5 and RS5 models as well as standard on the A8 - makes a dramatic difference in real-world performance.

So torque vectoring, at least the Audi rendition of it, works. Certainly, on slippery ice. We'll have to wait for another test of how much advantage it offers on dry tarmac, though Audi engineers assure us that the system's advantages are even more dramatic when the road is grippy. Of course, these are the same guys who were putting me to sleep with endless technical videos just the night before. They may have a bit more credibility now, however.