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Audi e Tron S Sport Back Prototype.

Can’t we already buy an e-Tron with electric all wheel drive?

Yes, the e-Tron debuted last year as Audi’s first all-electric vehicle, and does feature all-wheel drive, but it’s got only one motor per axle. Audi says the more powerful e-Tron S will be the first mass market vehicle to feature twin electric motors on the rear axle when it goes on sale later this year.

The benefit isn’t only 0-62mph in just 4.5 seconds, but a more rear-biased driving experience that includes drifty showboating, extra dynamic accuracy, and the ability to instantly take torque away from a single rear wheel if, say, one wheel finds itself on mud and the other dry tarmac.

How does it work?

It starts with the same asynchronous electric motors you’ll find on the e-Tron 55, which is the next step down in the range, and like all e-Trons has more power at the rear axle than the front. But here’s the twist: the S takes the 55’s rear e-motor and puts it on the front (for up to 201bhp), then takes two of the 55’s front e-motors and puts them on its rear axle (for up to 354bhp for the rear tyres). There’s space to fit those two motors because it’s all been in the plan since the beginning, five years ago.

All told, that gives 496bhp and 717lb ft available in ‘boost’ mode for periods of eight seconds, but even if you can keep your foot pinned for more than eight seconds to deplete boost mode, there’s still an extremely healthy 429bhp and 596lb ft on tap.

In normal driving, the front e-motor switches off, and only chips in when the driver calls for more acceleration, or the drive train senses slip.

So it’s just very fast in a straight line?

It is, but there’s more too. Because there’s one e-motor per rear wheel, the torque can be applied individually to those wheels. It’s called electric torque vectoring, and kind of works like a mechanical limited-slip differential, except there’s nothing but software linking the two motors. It also responds in milliseconds (up to a fourth quicker than a conventional system, says Audi), and can apply 162lb ft more torque quickly and seamlessly to the outside rear wheel in a corner than it does to the inner wheel. And because it’s electric, there’s also more torque being applied full stop.

Meanwhile, on the front axle, wheel selective torque control uses the discs and pads to gently brake the inside front wheel. It all helps rotate the car in to the corner, just as comparable systems do with internal combustion engines, propshafts, differentials and driveshafts.

All the motors and the software are designed in-house by Audi, with each e-motor supplied three-phase power current by its own power electronics. Co-ordinating everything is the Electronic Chassis Platform, ensuring every part of the triple-motor jigsaw does the right thing according to grip levels and driver inputs for a harmonious drive.

What’s the e-Tron S like behind the wheel?

It’s certainly got a broad skillset, from a small amount of confidence-inspiring under steer to flamboyant over steer if you select Dynamic mode and slacken the stability control system.

We’re lapping Audi’s Neuburg test facility in damp conditions on winter tyres, and the huge electric performance naturally means instant and nausea-inducing acceleration accompanied by nothing but eerie silence. There’s a clear rear bias to the e-Tron S Sport back but pressing on through a fast right-hander, the contribution from the front axle is clear – it pulls the e-Tron through the apex as the rear tyres edge towards their limit, and there’s just a little under steer as that power pulls you out. It gives you confidence to lean on the front end and push harder.

It’s also impressively serene at the wheel, despite our rapid progress – partly because electronic torque vectoring is acting at the rear and selective wheel control at the front is helping to guide the car through the corner, reducing steering inputs.