Drive On: GM's aerodynamic pickup truck is no oxymoron

As oxymorons go, "aerodynamic pickup truck" ranks right up there with" military intelligence" and "jumbo shrimp." But General Motors thinks it can prove that it accomplished the task on this one.

We'll believe when we see it -- in better gas mileage numbers for the shapely new trucks.

But it is interesting to hear how GM went about making aero improvements to the new 2014 GMC Sierra and Chevrolet Silverado full-size pickup trucks. GM says it went over inch of the trucks an effort to find places to make air slip more easily over the truck's steel body.

"We can't stop air," says Diane Bloch, an aerodymanics performance engineer. "We can only guide it through the path of least resistance."

Here are the highlights:

--Air dam. A new air dam beneath the front bumper directs air away from the trucks rhough underbody, which creates extra drag.

--Tailgate. The top of the pickups' tailgate and a center stop light are positioned in a way to keep air flowing freely.

--"The gap." There's a gap between the cab and the truck bed that becomes a place where air can become trapped. To keep it from happening, a seal was added.

The drive to create a more aerodynamic truck also led to the solution of a mystery. The issue was whether a tailgate raised or lowered is better for aerodynamics. Tests showed that truck is more aerodynamic with the bed gate up.