Inspiration: Audi quattro
The quattro was the car that made performance four-wheel drive popular - at the same time reinventing Audi's image
Audis were solid, sensible, dependable - and a bit dull - until the quattro came along in 1980. It redefined performance road cars, and together with the aerodynamically efficient 100 which followed it in 1982, the quattro succeeded in repositioning the Audi brand as a technology innovator.
Four-wheel drive itself was nothing new. Off-roaders like the Jeep and Land Rover had used it for decades, and the multi-role Range Rover had been around since 1970. Even before that there had been experiments with four-wheel drive for performance cars, notably in the 1960s when the Jensen FF and a handful of unsuccessful four-wheel drive F1 and Indy cars appeared - and were rapidly abandoned.
When a car corners, its inside wheels take a tighter line than its outer wheels, so the outer wheels have to travel faster to keep up. The differential feeds power to both driven wheels while allowing them to rotate at different speeds. In a four-wheel drive transmission there naturally have to be differentials front and rear, but because the rear wheels tend to follow a tighter line than the fronts there must also be a central diff to allow for differences between the speeds of the front and rear axles. These additional diffs add weight, and most engineers concluded that four-wheel drive systems were too heavy, bulky and inefficient for use in performance cars.
Audi's breakthrough came when Volkswagen designed an off-road 4x4 called the Iltis in the mid-1970s, largely by plundering the existing Volkswagen/Audi parts bin. Experience with the Iltis led Audi engineers (notably Ferdinand Piëch, now Volkswagen chairman) to investigate the benefits of four-wheel drive in a high-performance road car, starting with a B2 Audi 80.
Established Audi practice was to hang an in-line engine longitudinally in the nose, with the gearbox behind the axle line and the final drive to the front wheels between them. The clever part of the new four-wheel drive transmission was that the gearbox output shaft was hollow, and drove a pinion cage of the centre differential (actually a modified Audi 50/VW Polo diff) at its rear end. The pinions drove a pair of bevel gears, just as in a conventional differential. One bevel gear took drive to the rear wheels, while the other was connected to a shaft which ran forwards, though the centre of the hollow gearbox output shaft, to the front axle. The result was an amazingly light and compact system which permanently drove all four wheels.
Even with four-wheel drive a single wheel with no grip could still halt progress if the centre and rear differentials were in their normal 'open' state, so the centre and rear diffs were provided with dog clutches to lock them for optimum traction in severe conditions.
Back-to-back tests with standard front-drive cars demonstrated the expected traction benefits. Because each tyre was called upon to transmit less tractive effort, the chances of a wheel spinning were much reduced. Testing also proved another benefit: tyres generated less rolling resistance when driven gently than when rolling freely, and the difference was more than enough to offset the additional frictional losses of the four-wheel-drive transmission. Prototypes achieved higher maximum speeds when driven by all four wheels than when the rear driveshafts were removed.
Convinced by the performance of the prototypes, Audi management gave Piëch the green light to develop a high-performance, four-wheel drive machine for road and rallying.
The new car was powered by Piëch's favourite engine, the in-line five-cylinder developed for the 100 in the mid-1970s. A 170bhp turbocharged version was already under development for the 200 5T saloon, but for the quattro it gained an intercooler and an electronic ignition system with an intake air temperature sensor and a fatter exhaust system. Maximum boost rose from 0.75bar to 0.85bar - about 12psi - which increased output to 200bhp at 5500rpm.
At its Geneva launch the quattro (Audi generally preferred a lower-case Q) was the talk of the show. Pugnacious wide-arch styling (by Martin Smith, now Executive Director of Design for Ford of Europe) and technical sophistication wowed the crowds. Press road tests soon confirmed the quattro's awesome ability in tricky conditions, though considerable criticism was levelled at the lethargic engine response at low speeds. Motor magazine revealed that at full throttle in fifth gear a quattro was slower from 20 to 60mph than a 900cc VW Polo, but from 60 to 100mph it was quicker than a Porsche 911SC!
Four-wheel drive traction made the quattro a promising rally car, once Audi's lobbying (along with Renault and Lancia) to lift a ban on all-drive entries succeeded. Works quattros made an inauspicious debut at the Monte Carlo Rally in 1981 when Michele Mouton retired with fuel system woes and Hannu Mikkola crashed out of the lead, but the Audis were soon winning. In 1982 Audi won the manufacturer's world title and Audi Sport UK's rally quattro won the British championship in the hands of Mikkola and Arne Hertz.
Roadgoing quattros were left-hand-drive only, but right-hookers appeared late in 1982. Pneumatic (rather than cable) operation for the diff locks arrived the following year, along with anti-lock brakes and revised gear ratios. In 1984 the quattro was given wider wheels, stiffer suspension and a gimmicky talking digital dashboard. By then Lancia were beating the rally quattros with the lighter, purpose-built 037 Group B car, so Ingolstadt hit back with its own Group B machine, the Sport quattro. Sacrificing some of the original quattro's generous interior space with a 320mm wheelbase chop and swapping steel panels for composite, Audi saved weight and made the Sport quattro a more wieldy rally machine. An alloy engine block contributed to the weight saving, and on top sat a new 20-valve head which helped boost the road version's power output to 304bhp, and the works rally cars to around 450bhp.
The road car was given a 2226cc engine in 1988, controlled by a Bosch engine management system incorporating a knock sensor which allowed the compression ratio to be raised. Peak power and torque figures were unchanged, but that off-boost tardiness was now reduced. A Torsen centre diff was fitted, to replace the old manual diff-lock, and the manually rear diff lock now automatically disengaged above 25km/h (about 15mph).
A twin-cam, 20-valve cylinder head appeared in 1990, raising the quattro's power output to 220bhp and providing 228lbft from just 1950rpm. With the extra power of the 20-valve engine and the traction of four-wheel drive, the quattro could beat six seconds for the 0-60mph dash, though its top speed was a less impressive 143mph - due in part to the upright high-drag shape. Production continued until 1991 when it was effectively replaced by the S2 quattro, an altogether softer machine based on the aerodynamically superior Audi 80 coupe. While the new car's modern looks made the original car (known in Germany as the 'ur-quattro') look all of its 10 years old, many still thought the old stager was the better machine.
The quattro spawned a whole generation of four-wheel drive performance cars from Lancia, Ford, Vauxhall-Opel, Peugeot and others. Four-wheel drive quattro drivetrains have spread throughout Audi's range and four-wheel drive systems are also used elsewhere in the Volkswagen empire - from Skoda to Bugatti. But it all started in 1980 with the quattro.