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25 Jul 2018

Getting a grip

Harnessing increasing performance with the ingenuity of all-wheel drive.

Harnessing increasing performance with the ingenuity of all-wheel drive.
Amid all the fanfare surrounding 70 years of Porsche sportscars, Zuffenhausen has marked another anniversary this summer: 30 years of all-wheel drive. Criticised on occasion for its additional weight and handling compromises, Porsche’s four-wheel drive system has nonetheless become a mainstay, not just in its hugely successful SUVs, but in its flagship performance cars.
Porsche’s association with four-wheel drive is actually remarkably old, stretching further back than the marque itself. The first ever four-wheel drive car to carry the Porsche name was a petrol-electric hybrid, designed by Ferdinand Porsche at the turn of the century for Austrian coachbuilder Jacob Lohner. The Lohner-Porsche, as it became known, was
‘a four-seat horseless carriage’ with both electric and petrol power and four-wheel drive.
Half a century later, the Type 360 was designed by Porsche for the fledgling Italian sports car company Cisitalia. Another technological tour de force, it featured a supercharged flat-twelve making over 300bhp with its power switchable between rear and all-wheel drive configurations via a sequential manual gearbox.
Way ahead of their respective engineering epochs, both cars were too complicated for the production processes available to them in period. So it would not be until 1981 that Porsche returned to the subject of four-wheel drive, this time taking the matter of delivering on design into its own hands.
At the Frankfurt Motor Show, an all-wheel drive 911 Turbo Cabriolet was unveiled. Although technically just a concept, it was based on a standard 930, suggesting that a real world all-wheel drive system for series cars could well be in the pipeline.
The flames were fanned further in 1984, when Porsche decided to launch a new works rally programme with the Type 953. This beefed up but otherwise recognisable 911 featured an advanced part-time all-wheel drive system, designed to take on the glamorous yet daunting Paris-Dakar Rally. Porsche entered three cars into this most grueling of races, winning it outright at the first attempt.
Motorsport has always been Porsche’s preferred arena for development, and the rallying arena would prove the perfect playground for phase two. In 1986 Porsche unveiled the 959, a Group B car prepared for the Dakar and endurance racing. It’s dominance of both series was cut short by the cancelation of Group B, however, and Porsche was left with its loss-leading homologated road cars to sell.
But sell they did. The 959 was so advanced that some of its onboard tech would take twenty years to become the industry norm. Here was a 200mph supercar with more civility than a contemporary family saloon. It was also a performance totem like no other, harnessing all-wheel drive to maximize traction and grip via electronically controlled torque distribution.
The 959 not only paved the way for Porsche to develop an all-wheel drive system for full series production, it also sold the concept to the sceptics. No longer the preserve of hillside farmers or moustachioed rally drivers, four-wheel drive was suddenly sexy – desirable tech with genuine racing provenance.
This breakthrough could not have come at a better time for Porsche, in terms both of its design evolution and public perception. The increasingly powerful and popular 911 was proving something of a liability in the hands of the uninitiated, and Porsche needed to nip the notion in the bud that this was a ‘dangerous’ car.
By the mid-Eighties Porsche’s engineers were preparing a new generation of 911 for market that would be a huge departure from the G-Series. The Type 964 was more complex, more civilized, and more complete than anything to have gone before, and it would be offered as a ‘Carrera 4’ for the first time.
Porsche referred to its new system on the ’4’ as a ‘differential slip-control’, meaning that torque was distributed via a longitudinal transfer case and enclosed transaxle shaft with a 69:31 rear bias. Slippage at individual wheels was detected by the ABS sensors and prevented by hydraulic locks.
In 1994, for the Type 993, Porsche simplified the system to make it lighter, favouring direct rear drive with a viscous coupling sending power up front in the event of a speed variation in the axles. This better replicated rear-wheel drive, but with increased safety, less complexity and a reduced weight penalty. So effective was this new technology that it would carry over to the 996 a few years later, with the new water-cooled Carrera 4, 4S and Turbo all go-to daily drivers as well as widely respected performance cars.
Today, Porsche’s all-wheel drive is a dizzyingly complex system with electro-hydraulic actuation of a multi-plate clutch and the latest Porsche Traction Management improving both handling and fuel efficiency. But for all the perplexing tech, the end game for the consumer remains the same: more power, more of the time. All very Porsche.

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