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A textured surface will have lower drag, and therefor, be more efficient, than a smooth surface, all else being equal. It would take some research to determine the right texture, but it could be done. However, most people seem to be forgetting that the myth was that a normal dirty car would get better MPG due to a dimple-like effect. The chances of normal dirt, dust, mud, and other road grime just happening to provide this effect are virtually non-existent. If the real world, the highly irregular pattern will add parasitic drag and lower fuel efficiency. Even if (or more likely, when) textured surfaces become common, dirt will affect MPG even more in the wrong direction.
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THAT Irving, Alex