Since the launch of Unbound Vol. 6: Head to Head, we have been riding the Audi hype train to celebrate the automaker’s return within Need for Speed’s digital world.

We have uncovered the in-game updates and even looked back on our top five tuned Audis featured on Speedhunters over the years. But for this week’s theme, we’re taking you all back to school… quattro school.

You’ll find a quattro variant of almost every production Audi in 2024. Yet its origins date back to the 1970s, with engineers Jörg Bensinger and Walter Treser widely credited for pioneering (and being the driving force behind) the technology ahead of its global debut in the 1980 Ur-quattro road car.

Then, as Audi rolled it out within their rallying campaign from 1981 onwards, it quickly became apparent this all-wheel drive revolution was here to stay. Not only did Audi claim two World Rally Championship titles and 24 victories between ’81 and ’86, but there hasn’t been a two-wheel drive winner of the WRC since Lancia’s 037 in 1983.

Audi’s quattro might be the most renowned all-wheel drive system on the planet, but it wasn’t the first of its kind – not by a long shot. Early four-wheel drive transmissions date back to the inception of the internal combustion engine. Dutch brother Jacobus and Hendrik-Jan Spijker paved the way in 1902 with their Spyker 60 H.P.

In the following decades,, several 4×4 systems were developed for military and off-road use, including the Willy’s Jeep and Series 1 Land Rover.

What about ‘normal’ cars? Well, Jensen’s FF from 1966 and Subaru’s Leone in 1971 both utilised all-wheel drive long before Audi joined the party. What made quattro different was how it powered all four wheels.

Rather than use a heavy, inefficient transfer box to drive both axles, Audi developed a lighter, smaller centre differential to deliver the power front and rear. Then, when traction became even more limited, the centre diff could be locked with a vacuum-operated button, allowing the front and rear diffs to rotate at the same speed without slipping.

But the real game changer came in 1987 when Audi introduced the Torsen (torque sensing) centre diff. Unlike other systems, this one allowed Audi to continually split the power between axles when needed. So rather than sending power 50:50, it could send anything from 25 to 75% to the axle with the most grip. That kind of tech seems commonplace now, but rewind nearly four decades and you can see why quattro gained such a reputation in both passenger cars and motorsports.

In 2024, the term ‘quattro’ now comes in multiple variations depending on model and intended use – some you’ll already be familiar with, others maybe not. So, grab a pen and paper; class is now in session.

Back in 1976, Walter Treser found himself as the head of Audi’s ‘Advanced Special Vehicles’ program. One of his earliest tasks was to oversee the secret development of an all-wheel drive, high-performance car as instructed by Audi CEO Ferdinand Piëch.

The project didn’t even have a proper name, with the original prototype model simply known as A1 (standing for all-wheel drive number one). What’s more, nobody beyond Piëch and the Audi engineers – including Treser and Bensinger – knew about the plan. Especially not Volkswagen.

The story goes that while chatting with Volkswagen’s head of chassis development in Ingolstadt, the engineer boasted to Treser about how great the handling was in their four-wheel drive, off-road VW Iltis, before quickly making an off-hand comment about how good it’d be if the Iltis could have even more power to outshine its rivals.

Hearing this, Treser became more intrigued with the idea of using all-wheel drive in a sporty passenger vehicle, either a coupé or two-seater. Piëch shared the same view, which ultimately became the foundation for Audi’s first four-wheel drive production car, the Ur-quattro. Ur means ‘original’ and quattro means ‘four’… in Italian.

However, the Ur-quattro was almost called something entirely different. Carat – short for ‘Coupé All-Wheel-Drive Turbo’ – was the name favoured by the Audi board, but due to this name already being used by a lady’s perfume brand, it was Treser’s previous suggestion (Audi quattro) that reigned supreme.

‘Torsen’ might sound like another Audi engineer, but the term actually means torque-sensing. It was this development in 1987 that truly revolutionised the way all-wheel drive transmissions work.

In the first Ur-quattro, an open centre differential was used with the ability to lock it manually via a dashboard switch. But from 1988 onwards, this was replaced by a Torsen differential – the Type 1 – which allowed engine torque to be sent automatically to either axle depending on which one needed it the most.

By default, the split offered a 50:50 distribution, but as grip or traction changed, up to 80% of available torque could be sent to either axle without any need for manual input.

This wasn’t without its limitations, however. Like a conventional limited-slip differential, the Type 1 Torsen is limited by the amount of torque that is able to be supplied to an axle. So if one axle has no grip, the other axle won’t be delivered substantial torque, either.

To try and combat this, Audi initially offered the second-gen Quattro with a manual-locking rear diff. Later advances (and a shift to electronically-controlled differentials) meant that each corner of the car could be monitored to limit wheel spin and allow torque from a low-traction wheel to be passed via the Torsen diff to high-traction wheels instead.

In the case of early quattro systems, Audi used a longitudinally-mounted engine with a centre differential to provide permanent all-wheel drive, with the ability to shift torque between axles with the Torsen centre diff.

But what about those predominantly front-wheel drive Audis? Simply, ‘Haldex’ refers to the name of the original manufacturer, and this drivetrain was designed to provide optional all-wheel drive on those front-wheel drive cars fitted with transverse-mounted engines. Think first-gen TT and S3 models, for example.

To keep the packaging tight, Haldex uses a multi-plate clutch at the rear differential (rather than a centre diff) to engage the rear wheels, when necessary, rather than being permanently driven like in earlier models. The downside? Because of the clutch positioning and the front wheels always being driven, earlier Haldex models could only send up to 50% of the available torque to the rear axle. This means that – for the most part – Haldex didn’t feel ‘properly’ quattro compared to the models before it, something Audi addressed later down the line…

For most modern Audis, quattro ‘Ultra’ is what’s commonly used. This (as the name suggests) is the best of both worlds, combining traditional torque-sensing with the ability to run front-wheel drive without the drawbacks.

Why would you want to mainly run front-wheel drive? Well, Audi found that 90% of driving doesn’t require power sending to all four wheels. Anyone who’s seen a dyno graph will know that all-wheel drive saps power, which in turn uses more fuel and reduces overall efficiency.

The solution? Use an electronically-controlled clutch at the rear differential (just like Haldex) but with another clutch also located at the transmission, disconnecting the driveshaft altogether. According to Audi, this improves fuel efficiency by nearly 20%.

The fun doesn’t stop there either with quattro ultra. By taking data obtained from the various sensors around the car (including GPS position and outside temperature), Audi’s quattro ultra system can even predict when a driver will require front or four-wheel drive without any other intervention needed.

So far, we’ve looked at quattro in transverse and longitudinally-mounted forms. But what about the oddity to the range – the mid-mounted, V10-powered R8 supercar? Naturally, this has a unique quattro variation which uses an electronically controlled hydraulic multi-plate clutch.

Because of the heavy engine in the rear, by default, the R8 is rear-biased with a split of 85% to the rear axle and 15% to the front. But, when the grip or driving requirements change, an electric axial piston pump (which can build as much as 40bar of pressure in just a few milliseconds) presses the friction plates within the clutch together, allowing constant variation of torque between the front and rear axles.

In second-generation versions of the R8, this even allows quattro to distribute 100% of available torque to either the front or rear axle. But if you really want a rear-wheel drive R8, the R8 RWS built between 2017 and 2018 is your answer. It’s lighter, faster and permanent rear-wheel drive only.

That’s a lot of tech to digest in a short time, and we know this barely scratches the quattro surface before you point out what we’ve missed. But quattro is Audi’s party piece after all; this tech not only put them on the map back in the ’80s, but it continues to do so even into 2024 with more vehicles than ever boasting all-wheel drive.

Naturally, this prestige has yielded some pretty special quattro editions over the years, from the screaming IMSA GTO race car to the Le Mans-winning R18 e-tron. But if we had to choose just one? We’re going five-cylinder and five doors – the Audi RS2 Avant.

A fast wagon developed with Porsche that also boasted quattro in the early 1990s? Even by today’s standards, they’re obscenely cool – and fast.

Let us know your favourite quattro-equipped Audi in the comments section.

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