How Drag Affects Mileage
 

I found this web site - https://www.edmunds.com/advice/specia...4/article.html

"For a full-size truck, a change in drag coefficient of 0.01 is approximately equal to an improvement in fuel economy of 0.1 mpg on the combined city/highway driving cycle," says GM's Schenkel. "The same drag coefficient reduction can improve a car's fuel economy by approximately 0.2 mpg."

Interesting .. a reduction of a cars drag co-ef of 0.01 = +0.2Mpg