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MERCEDES MUSCLE: A Love-Hate Affair
By Thom Cannell

I can't stand it. Part of me despises this car, and with good reason. With its Active Body Control (ABC) electronics and hydraulically assisted suspension, it obviates driving skills I've worked for 20 years to develop.

With the spin of an electron, Mercedes has eliminated the necessity for carefully weighting the car on entering a turn, gracefully delivering a soupcon of weight to the brake pedal followed by an elegant application of throttle. Instead you simply steer and the CL500 will do a better job of balancing the chassis than you will ever achieve. And that is an assault on the human spirit, to be humbled by "chips and salsa" (circuits and software in "geek speak").

There is, on the dash of each CL500, a magic switch that transforms its suspension from merely assistive into actively assertive. It changes the action from 65 percent to 95 percent roll reduction. On the road, the difference between the two is readily felt, even by passengers. Either setting makes for pleasant driving -- city, freeway, or wherever you show off. But the lesser active setting is more comfortable in ordinary driving.

THIS ABC THING, the combination of high pressure (2,840 pounds per square inch) hydraulic servomechanisms (power amplifier) and the usual Mercedes level of chassis design are as flawless a suspension as I've felt testing on good smooth roads. What it means to a driver is no squat at the rear on acceleration. No dive at the front when braking. And little chassis roll when cornering. Each of these forces is an acceleration; all are dealt with quite competently.

Thirteen sensors monitor body movement, requiring two microprocessors. They control a hydraulic servo atop each coil spring. Input comes from a wheel sensor at each corner, one longitudinal and one transverse movement sensor, three vertical acceleration sensors, and one that determines level. As a benefit, the car is self-leveling in response to changes in loading (passengers and luggage) and can raise the car 12.5 millimeters and lower it the same amount at speed. This is never apparent.

Active Body Control modifies forces that take place below 5 Hertz, better thought of as jiggles that happen between once and five times per second. Ah, now it begins to make sense. Braking. Initial cornering. Stomp-the-pedal acceleration. All these chassis upsets are slow when compared with the abruptness of a pothole.

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