Once upon a time, the idea of sending power to all four wheels was reserved for utility vehicles that had to traverse demanding terrain. Usually this meant unpaved back roads in rural areas, though purely off-road conditions across untamed wilderness and/or snowy and icy conditions on both paved and unpaved roads were also popular circumstances for four-wheel-drive applications.
That was back when Willys owned Jeep and Land Rovers were primarily used for chasing koala bears across the outback. Subaru hadn't yet introduced us to the "beauty of all-wheel drive" (or the model "Outback") and the term "crossover" referred to former country/western singers who had gone mainstream. But by the time I wrote "What Wheel Drive?" back in 2000, the concept of making all four wheels pull their own weight had done its own mainstream crossover (and the automotive marketing term "crossover" was just making an entrance).
I've recently driven three all-wheel-drive vehicles that, despite being Chrysler products, continue to break from the original spirit of that Willys Jeep. These were the Chrysler Pacifica, the Chrysler 300 and the Dodge Caliber. Clearly none of these are SUVs in the traditional sense, but by driving them over varying paved and unpaved road conditions, in the mountain resort town of Aspen, I was better able to understand the differences between each vehicle's all-wheel-drive system.
Chrysler's Pacifica uses the most basic type of full-time, mechanical all-wheel system. It delivers torque to all four wheels all of the time, but allows the front and rear tires to rotate at different speeds. This makes for a smooth ride on dry pavement and around corners while still offering added traction over slippery surfaces. A viscous coupling attempts to equalize power between the front and rear wheels when either axle experiences slippage, and the car's traction control system can further reduce slip by applying individual braking force to a wheel that is losing traction.
Driving the Pacifica over deeply packed snow proved that its AWD system will likely keep the car from getting stuck. And while directional control was certainly better than on a two-wheel-drive vehicle, it was not as confident as those vehicles equipped with the more advanced AWD systems offered by Chrysler.
Case in point, the Chrysler 300 offers full-time, mechanical all-wheel drive that is similar to, but far more advanced than, the Pacifica's. Instead of a viscous coupling, the 300 uses a planetary gear in the transfer case to control wheel slip while distributing 62 percent of power to the rear wheels under normal conditions. Also, like the Pacifica, it uses the car's ABS and traction control systems to brake individual wheels when it senses slippage. But unlike the Pacifica, the 300 features all-speed traction control, meaning it will not only brake an individual wheel that is slipping but also cut engine power to a given wheel to enhance stability. This improves the 300's straight-line traction and, when combined with a steering wheel angle sensor, also keeps the vehicle "on course" when it veers from the driver's intended path. It's this combination of technology that provides the 300 with an Electronic Stability Program (ESP), something the Pacifica doesn't offer. The Chrysler 300's stability and traction control systems can theoretically be turned off, though they will still intervene under extreme circumstances to prevent a spin.
Driving the 300 over the same snowy road course as the Pacifica illustrated the differences between these two systems on several levels. First, while the Pacifica will generally not get stuck on packed snow, it will not maintain the driver's intended path with the same level of confidence or refinement that the 300 offers. Response time to wheel slippage is much slower in the Pacifica, allowing the car to rotate in unexpected directions and requiring greater care through corners to stay on course. The 300 not only reacts to driver inputs more quickly and smoothly but the ESP system allows for truly bone-headed behavior. You can, for example, basically floor the 300 and the ESP will cap engine power to match available traction, whether in a turn or traveling in a straight line. This can be a pain when trying to drive the car fast on dry, twisty roads — or at our test facility — but it's a literal lifesaver when navigating slick road conditions.
Dodge Caliber R/T
The Dodge Caliber's all-wheel-drive system lands somewhere between the Pacifica and 300 in terms of advanced features and refinement. Like the Pacifica, it utilizes individual wheel braking to enhance traction and stability; and like the 300, it offers steering wheel and throttle sensors as part of its ESP to help keep it pointed in the right direction. You can floor the Caliber on slippery surfaces and, as with the 300, it will reduce throttle input and match engine power with available traction. However, unlike either the Pacifica or the 300, the Caliber's all-wheel-drive system is not full-time. Instead, it uses an electromagnetic coupling to drive only the front wheels until slippage is detected, at which point power is directed to the rear wheels.
Scooting around the snowy road course in Dodge's Caliber R/T effectively displayed the advantages of combining part-time all-wheel drive with a relatively advanced ESP system. For a sub-$20,000 hatchback, the Caliber felt considerably more capable than the Pacifica, though it wasn't quite up to the 300's confidence level (probably because of the 300's heavier weight and longer wheelbase/wider track). With its seamless distribution of power between the front and rear wheels, the Caliber R/T proved itself a worthy year-round mount for buyers living in cold climates, despite the car's performance-oriented image. It's also encouraging to see this level of advanced all-wheel drive trickling down to the economy-car segment.
Regardless of any given system's technical makeup, it's clear that automakers are supplying this technology just as consumers have come to demand its availability on an increasingly wide spectrum of vehicle types. The Pacifica is a crossover, the 300 is a large sedan and the Caliber is an economy hatchback. Not an SUV in sight, but all of them offer AWD and none of them use the same AWD system.
What does this mean for our future? Is all-wheel drive the next keyless entry or MP3 capability? Will it become as commonplace as oversized wheels or Sopranos reruns? As someone who first discovered the beauty of AWD on a 1991 Dodge Stealth R/T Twin Turbo, I hope the answer is yes.