For many drivers, being able to get where they want to go when they want, regardless of weather conditions, is the ultimate automotive luxury. Automakers answered this demand with a number of all-wheel-drive systems that started showing up in the 1980s.
All-wheel drive is different from four-wheel drive in that it has only a single gear ratio and no low-range position in the transfer case. Without low range, extreme off-road driving isn't possible, but AWD can still provide far greater traction and control on snow or ice-covered roads than two-wheel drive. Over the ensuing years, manufacturers refined their offerings and added electronic controls that make these systems operate faster and more effectively, further improving traction and safety.
Mercedes-Benz recently used the 100th anniversary of its first all-wheel-drive system to announce its latest version of 4Matic and to showcase the brand's lineup of AWD models. American buyers can now get the 4Matic system on 18 models in seven classes, including on several SUVs.
The newest iteration of 4Matic, introduced on the 2007 Mercedes-Benz S550, is an all-new design and may also be used in upcoming R-, GL- and ML-Classes.
Mercedes' goals for this newest 4Matic were to minimize size, gear noise, weight, and drag, while improving driving dynamics. A smaller transfer case integrated into the rear of the seven-speed automatic transmission eliminates one complete gear stage. The transfer case utilizes a center clutch that serves as a limited-slip differential, allowing the front wheels to rotate faster in turns. (All Mercedes SUVs except the G-Class have non-locking differentials, and lockers are optional on the GL.)
For 2007, the new 4Matic system uses a stronger multiplate "breakaway" clutch; other models have a single-plate clutch. Power is now divided between front and rear wheels at a fixed ratio of 45/55 percent and the system has no electronically controlled clutches, which increases reliability.
Installing the rear U-joint of the front driveshaft into the output gear places the shaft close to the transmission. Power from the front differential goes to the left-front axle via an intermediate shaft that runs through the oil pan. This more compact design allows this system to fit on the standard chassis without intruding into the front-passenger footwell. Total weight of the 4Matic is only 159 pounds, and it's claimed to lower fuel economy by less than two mpg.
How does it perform in the real world? After driving all the current 4Matic models plus the G-Class, which uses a more-conventional 4WD system, what stood out most was how transparent 4Matic is during operation. And, other than the trunklid emblem, it's difficult to tell the 4Matic version from the standard model. They look identical to rear-drive models inside and out. In dry conditions, 4Matic makes little difference in driving performance. Its incremental extra weight didn't noticeably slow acceleration, and handling feel is unchanged. However, on ice or snow, you can feel the 4Matic and electronic aids gently trying to save and even guide you, directing power to the tires with traction and touching the brakes ever so slightly on various corners to keep the vehicle on course. Everything's subtle, without any lurching or wheel binding; there's just an occasional pulse of the ABS.
Although Mercedes' AWD systems are designed to think for themselves and reduce the driver's workload, there are some things you can do with these and other systems to optimize their performance. Read the owner's manual and thoroughly familiarize yourself with your vehicle's system and factory recommendations and warnings. Regularly check your tires for condition, tread depth, and proper inflation. When driving in slippery conditions, look far ahead and plan your moves, anticipating changes in traction, gradient, and curves. Get the right set of tires. The weakest link with 4Matic-equipped vehicles was their all-season tires. If you plan to do a lot of driving in mud or deep snow or on ice, consider changing to more aggressive tread.