FOUR RINGS, FOUR TIMES THE FUN
Arguably the industry leader in all-wheel drive is Audi. The German automaker introduced its famed quattro system in the spring of 1980 on a two-door car of the same name. It was the first volume-built permanent all-wheel-drive setup suitable for sporty vehicles, and that focus on driving performance continues today.
On the first-generation quattro system torque was split evenly between the front and rear axles. Under its boxy hood sat a longitudinally mounted engine, but the car featured at least one major innovation: a bevel-gear center differential. This complex-sounding part pulled double duty, directing power to the car’s front wheels and eliminating the need for a transfer case and auxiliary shaft, two heavy and complicated components.
In its day the quattro was quick and responsive, a Cold War driving sensation. Owners could also manually lock the center and rear-axle differentials for better traction on slippery surfaces.
Some three decades later, quattro is still an automotive institution. It’s gone through numerous iterations, sprouting torque-sensing differentials and electronically controlled hydraulic clutches along the way. But it’s still a leader in its segment.
When Audi develops a new vehicle, quattro is included from day one, something its competitors don’t necessarily do. In the words of Mark Dahncke, Product and Motorsports Communications Manager for Audi, competing systems are “engineered into the platform after the fact.” He said including all-wheel drive from the start gives Audi “a very, very cohesive system” that “works together.”
How these systems are attached to a vehicle’s powertrain is a big deal too, and Dahncke said they’ve got the manufacturing experience to bring everything together in a unified package, similar to AAM’s one-stop-shop approach.
Barrett said quattro is very complex, but also very compact because the system’s all-wheel-drive components are actually packaged inside the transmission, which keeps things as tight as possible. According to him the layout is unique to Audi.
“Frankly it’s the most expensive system,” Dahncke said, noting that quattro is still mechanical, “not just an electronic chip.” It’s always engaged — a true full-time system — shuffling engine torque from axle to axle and wheel to wheel, maximizing grip and minimizing slip. But Audi is not the only game in town.
THE BEAUTY OF SYMMETRY
Subaru proves there’s a lot more to all-wheel drive than just four wheels turning. Audi’s cross-hemisphere rival prides itself on delivering this technology to a mass market.
“It’s standard on all of our vehicles except the BRZ,” said Dominick Infante, National Manager Product Communications for Subaru of America, Inc.
In a move similar to what Audi does, Infante said, “all of our cars are designed to be all-wheel drive,” noting that they engineer it into vehicles from the get-go. Subaru calls its system “Symetrical All-Wheel Drive” because of how it sends the power to the wheels.
Competitors often retrofit all-wheel drive onto existing front-wheel-drive vehicles. With a transverse-mounted engine torque has to be transmitted around corners to drive the wheels, which complicates things and reduces efficiency – not so with Symmetrical All-Wheel Drive.
Subaru has several different versions of its system. Cars equipped with manual transmissions feature a set 50:50 torque split front to rear. Models powered by their 3.6-liter six-cylinder engine use a different setup known as a Variable Torque Distribution system – VTD for short. Subarus with continuously variable transmissions use yet another version, as does the outrageously quick WRX STI. Interestingly the STI allows drivers to choose how the torque is split between the front and rear axles so they can customize how the car behaves, whether they’re navigating a snow-covered mountain road or bombing around a race track.
Despite these different technologies Infante said, “we only have full-time all-wheel drive,” contrasting it with some of the competition’s systems that aren’t as robust and can’t put as much torque to the rear wheels. “With Subaru everything has to be a little bit overbuilt” he said. “It’s kind of the Subaru way.”
“X” MARKS THE SPOT
Swapping sushi for spätzle, another one of Germany’s automotive crown jewels has its own take on all-wheel drive. BMW has earned a reputation for building cars with unassailable dynamics, and its xDrive system lives up to this standard.
A full-time setup, it features a defined torque split favoring the back axle. Under normal conditions either 60 percent or 80 percent of the torque is sent to the rear wheels, depending on the vehicle.
When conditions dictate, xDrive can deliver all of the engine’s torque to the back tires and at least 50 percent of it can be shuttled to the front axle for extra grip in slippery situations.
In keeping with current industry trends, General Motors overwhelmingly favors part-time all-wheel drive. In fact, the only vehicles in its vast stable that are offered with a full-time system are big trucks – the Cadillac Escalade, GMC Yukon Denali and Yukon Denali XL.
All other systems the company offers are on demand – they only engage when wheel slippage is detected.