[masraum]

Originally Posted by Por_sha911

If you really want to boost the mpg's, remove the rear tailgate. Look at it like a giant parachute catching air and slowing you down as you drive.

I thought that and lots of other folks have thought that. The mythbusters even tested it and asked Ford Truck design engineers if they could explain it. Yes, they did explain it. IIRC, the air that goes over the top of the vehicle creates a clockwise swirling vortex in the bed. That vortex has a similar effect to making the truck a fastback. The air that isn't part of the vortex flows right over the back of the vehicle. They said that opening the tailgate actually reduces the effect and hurts the drag of the truck.