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The Mercedes-Benz W208 Chassis Design
One of the nice things about buying a Mercedes-Benz is you're getting a vehicle who's research and design was done by a competent engineering staff with an ample budget. The suspension design for the CLK430 is no exception. At the design stage, careful attention was paid to building a vehicle with the best combination of handling ability, road feel, and ride quality. It's structure was initially designed to accommodate both coupe and convertible bodies. That yielded a coupe with an exceptionally rigid structure. This rigid structure is the cornerstone that allows the CLK to be responsive and safe handling, yet retain a smooth, well-damped ride at the same time. This unusual dual personality has prompted some journalists to characterize Mercedes as "a sports car disguised as a limousine. "
That's all be true, but unfortunately it sounds like advertising. The real question is, "What's a good suspension design? " You've heard the hype. Fully independent, specialized shock valving, reduced spring height, blah, blah, blah. Every manufacturer has a reason why "their " particular sway bars, shocks, and springs are the "best ". The fact is, rarely is an ad produced that speaks of "suspension design ". The ads frequently speak of "parts ". Even then, most ads don't tell their audience what they really what to know about those parts. For example, suppose an ad stated a new sport model had 5% bigger sway bars. A buyer may assume that to be good, but how do they know? If the bar is too thick, the car will ride like an empty fire truck. If the bar is too thin, the car will sway like a sail boat in a squall. So what's the right size for the bar? The answer is, "It's vehicle specific. " Ditto for the springs and shocks. This means the buying public has to hope that the manufacturer's R&D team got the specs right for each of those parts. Even then, none of those parts can overcome an inferior design - the same design that regularly glossed over while the focus is shifted to "parts ". Mercedes-Benz is one of the few manufacturers that discusses "suspension design " in their ad campaign. Here's why:
The back of a CLK is anchored by the Mercedes-Benz patented five-link independent rear suspension. This design was first introduced for the 1983 model year on the 190 series. This renowned five-link system has since been used on many Mercedes-Benz passenger cars. The beauty of the five link rear is that it allows independent tuning of ride comfort and handling characteristics. This independent tuning is dynamic enough that it can be used on opposite ends of the vehicle spectrum - in both the S class and the SL. The five links are attached to each wheel in a manner that allows the wheel to cede to dynamic forces, yet not produce any rear wheel steer. That allows the system to maintain a proper tire/road relationship while the rear wheels rise or drop, in relation to the chassis.
Out front, the CLK’s W208 chassis uses an unequal length, double wishbone suspension system. This is quite a bit different than the three point MacPherson strut design that's so popular in the industry. The main advantage of a double wishbone design over a MacPherson strut design is in a curve, an unequal length double wishbone suspension will rotate in a manner such as to induce negative camber on the outer wheel. In plain English, cars have a tendency to lean while cornering. An unequal length double wishbone suspension does a better job of keeping the tires straight up and down, staying in full contact with the road. With a MacPherson strut design, the suspension leans with the car, the tires lean with the suspension (positive camber), and traction is lost because the tire is no longer perpendicular to the road.
An unequal length double wishbone suspension works by having an upper control arm that's shorter than the lower one.
With this configuration, when the wheel travels upward, the top of the wheel tips inward, gaining negative camber. It
works this way because the upper arm swings through a shorter arc than the lower arm. This pulls in the top of the tire
as the wheel travels upwards. This is what creates negative camber. It's this negative camber that keeps the wheel
in an upright position, and the tread flat against the road.
This begs the question, why do manufacturers use a three point MacPherson strut design if a better design exists? The MacPherson suspension design has fewer parts, is less expensive to manufacture, is extremely compact, and allows for smaller overall chassis dimensions. A smaller chassis means less weight. This light-weight small chassis is perfect for inexpensive small cars.
The unequal length double A-arm design has no functional disadvantages and is currently the most advanced suspension design available. Being the best design available, Ferrari uses it in every car they currently build. The only cars that don't feature this design are vehicles where price and space are of more concern than performance.
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© Marcus B. Fitzhugh 2005
Mercedes-Benz Specifications