Quote:
Originally Posted by ME_Andy
Fill me in, is rear lift good or bad for mpg?
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The rear section of many vehicles is sloped downward. Aerodynamic force acting on that surface will have a force vector perpendicular to the surface. Since the surface is sloped to the rear, the force vector will be angled to the rear as well. In other words, that lift also creates drag. The image below should help to visualize it.
That said, when designing a drag spoiler you also need to consider the rear wake. For example, if you make the angle of attack too aggressive, you'll increase the size of the wake. And that will create more drag.