Drag Coefficient (Cd) is a major component of a vehicle's aerodynamic drag. The others are frontal area and vehicle speed. Since speed is up to the driver engineers only have control over Cd x Frontal Area. It is also linear, meaning its impact on drag does not change with speed. Weight is another fuel economy factor, mostly in stop-and-go driving.
Apparently the new E-Class coupe has a 0.24 Cd. Not sure what the frontal area is but it is a medium-large car. As long as the cars don't get much bigger (and the tires too sticky), the drag reductions will result in real fuel economy benefits.
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Labels: cd, coefficient, drag, Mercedes