projection table calculator
 

One of the fun things I did with my truck on the calculator was enter the assumptions for my truck if I did a belly pan. If that could lower the Cd to 0.26 then the hwy mpgs would rise to 26 or 27 mpgs. At 75 mph a 22 mpg would be obtainable. It is fun to feed in hypothetical vehicle platforms to see what numbers fall out.