[aerohead]

In 2012, Frank Meinert, of GM Pickups, shared a ballpark metric with Edmunds.com.
Meinert suggested that, with 2012 pickups ( Cd 0.412 ), that any delta- Cd 0.01 drag reduction would translate to a 0.1-mpg improvement.
This is for EPA Composite mpg.
It works out @ delta-10% aero = delta-1.8% mpg.
EPA Highway would be higher.
Constant highway speed testing would be even higher.
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The Rocketail Wing researchers were using Delta- 10% drag = 4.8% mpg, very close to the old 10-5 ballpark.