All roads lead to Audi
Dynamic, fast and frugal, Audi’s new A4 Allroad Quattro offers a sophisticated ‘ultra’ system that predicts when all-wheel-drive is needed, reports Charles Rangeley-wilson
AN unfortunate side effect of the language barrier and the intensity of the technical tsunami my Audi engineer was attempting to render into English was that I was giving a good impression of being an idiot, incapable of understanding even the most basic ideas behind the workings of a motor car. Thus, I was relieved when, in the wettest interlude of the Bavarian rainstorm Audi had laid on to illustrate the efficacy of its new ‘Quattro mit ultra technologie’, I thought of an analogy our Audi guru had never heard of.
I was trying to get my head around what the ‘ultra’ bit did on this new A4 Allroad, when the lightbulb came on. ‘It’s like double de-clutching,’ I exclaimed triumphantly. Now, it was his turn to look baffled. ‘It’s how you change down gear in vintage cars,’ I explained, trying not to look smug. ‘You have to spin up the gearbox to stop it grinding, so you let out the clutch as you go through neutral and give the throttle a blip.’
I was always going to like this car, largely because I drive the older model and I’d say she’s second favourite only to my long-missed
This 4WD offers real savings on the drinks bill
Peugeot 205 GTI. This new version was like mine, only more so—dynamic, but not frenetic; refined, but not boulevard; fast, but not insane; frugal, but not sanctimonious.
Yes, there’s sharper steering in a BMW, more room in a Volkswagen and the A4 version of the Allroad is really a macho A4 in heelraisers. However, if you want allwheel drive (AWD) because you live where the roads are often covered in turnips and you go down rough tracks as often as you drive to London, the A4 Allroad is a great car.
Now, back to the technical befuddlement, because the really interesting thing about the new model is under the floorpan and, to see why, we must waltz through the pros and cons of four-wheel drive (4WD).
Most people who have ever put fuel in one will know that a big drawback of cars with permanent AWD is how much they like their drink. It’s thirsty work running those two extra wheels and their drive shafts, pinions and widgets. You might have traction when you need it, but you also have a hole in your wallet each time you nip to the fuel pump.
That’s why ‘soft-roaders’ (such as Volvo’s XC series and Range Rover’s Evoque) have a special clutch behind the gearbox that feeds power to the rear wheels only when the front wheels start to slip, which gives better fuel consumption, even if the reactive system isn’t exactly pure 4WD. Plus, the drive shafts and pinions of the rear wheels turn even when they’re not engaged—and all that friction still impacts on fuel economy.
Audi’s attempt at the 4WD holy grail—instant, predictive 4WD traction, but closer to 2WD economy —lies in a system akin to double de-clutching, in which, most of the time, only two wheels are driven. When power is needed at the rear, a clutch spins up the drive shaft and a second snaps two castellated wheels together in the rear differential. It’s very clever and happens in a maximum 250 milliseconds. Vitally, the system doesn’t wait for the front wheels to slip before engaging.
As my Audi engineer boasted, I wouldn’t be able to spin the wheels, even if I stamped on the throttle in a puddle, because a smorgasbord of computers monitors everything about the car and the way it’s driven to ‘predict’ when AWD is needed.
Usually, I’d reserve a dissection of differential internals for the midnight slot on Radio GreaseMonkey, but ‘mit ultra’ is worth the oily diversion. It appears to offer the best of both worlds— a 4WD system that’s effectively ‘permanent’, that is predictive, not reactive, and which offers real savings on the drinks bill. Perfect! Make mine a double.