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"         Mercedes-Benz&amp;#039;s legacy of building all-wheel-drive vehicles goes back 100 years, to the Dernburg Wagen of 1907, a massive 3.6-ton Touring Car used in German Southwest Africa (now Namibia) by Bernhard Dernburg, the State Secretary of the German Imperial Colonial Office. With permanent all-wheel drive and all-wheel steering, the tall gas-engine vehicle must have been quite a sight, able to climb 25-percent grades while taking Dernburg around the country on his official duties. At some point in the African post-colonial era, the whereabouts of the Dernburg Wagen became a mystery, and remains so to this day.   More recently, all-wheel drive has been quite a success story at Mercedes, the Stuttgart company now building 48 awd models across seven model series worldwide. And of these, the new S550 4Matic, now on sale in the U.S., draws our attention.   This is the first new W221 S-Class with 4Matic and the first 4Matic Mercedes passenger car with a 7-speed automatic transmission. Unlike the previous 4Matic, in which the transfer case was an independent unit aft of the transmission, the all-new version-developed in-house-has one integrated into the tail section of the 7-speed gearbox, even sharing the gearbox&amp;#039;s automatic transmission fluid. The torque split is now fixed at 45 front/55 rear (the previous S 4Matic was 40/60), and a multiplate &amp;quot;breakaway&amp;quot; clutch in the center differential serves as a form of traction control by limiting the power to all four wheels on slippery surfaces. What&amp;#039;s more, by dispensing with one complete intermediary gear stage, Mercedes has made 4Matic more compact and efficient, to great benefit.   First, the new 4Matic system is lighter, adding just 145 lb. to the weight of the car, whereas the old system added 220 lb. Second, because the driveshaft going forward to the front differential stays nearer to the transmission, there&amp;#039;s no longer a bump in the footwell of the front passenger. This means the new car is now built on the same body-in-white chassis as the rear-drive S-Class; further reducing the build complexity is a 4-link front suspension that&amp;#039;s identical to that of the rear-drive car. Also noteworthy is the drive to the left front wheel; as before, it&amp;#039;s via an intermediate shaft running through a channel in the engine oil sump.   With reduced weight and friction comes improved mileage. In fact, Mercedes says the S550 4Matic system burns only 0.4 liter of extra fuel per 100 kilometers traveled versus the conventional rear-drive S550. With the previous S, the 4Matic consumed an extra 1.0 liter of fuel per 100 km. In terms more familiar to Americans, the current rear-drive S550 is rated at 16/24 mpg by the EPA, whereas the new 4Matic is rated at 15/22, so gasoline costs will be a bit higher. Also realize that 4Matic adds about $3000 to the cost of a current S550, which starts at $86,175.   That&amp;#039;s a lot of money, but this is a lot of car. All amenities are present, and this is an automobile that makes 80 mph feel like 50, yet still manages to involve its driver. It feels just like a rear-drive S-Class with no untoward effects on the steering, and the 7-speed automatic shifts with an uncanny smoothness. Buttons on the back of the steering wheel allow for manual shifting, and in Sport mode the car holds gears until redline. Self-leveling Airmatic suspension delivers a comfortable well-damped ride with noticeably different driver-selectable settings, while Active Body Control continues to make excessive body roll in corners a thing of the past.   As you&amp;#039;d expect, the new S550 4Matic shines as a dignified and spacious 5-seat cruiser, beautifully built and loaded with electronic safeguards such as ESP stability control, 4ETS traction control and seatbelts that automatically tighten under strong deceleration. And when you are using the optional radar-based Distronic Plus cruise control, Brake Assist Plus will warn the driver if he or she is approaching a vehicle too quickly, and automatically apply the brakes if a collision is imminent.   You can bet the 1907 Dernburg Wagen didn&amp;#039;t have that feature; nevertheless, it was ahead of its time, just like the new S550 4Matic sedan. "^^<http://www.w3.org/2001/XMLSchema#string>
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