[Jackpine]

I think it does, but it would take a wind tunnel test to verify this. I base my opinion on the shorter drop from the top of the cab to the surface of the cover, which should create a smaller stagnation point there.

Removing the tailgate will probably have no effect. If you ever notice a piece of paper or plastic bag in the bed of a pickup with a tailgate, you'll see it moving around, but hardly ever getting blown out. There is kind of a "whirlpool" effect in the bed that doesn't let air in or out. Removing the tailgate just moves the big stagnation point up to the rear of the cab. And, you get interference effects along the upper top sides of the bed all the way to the rear. There will still be a whirlpool, it will just occupy a smaller space.

But, a cover does eliminate the "whirlpool" that takes energy to create. This energy has to come from somewhere and it is being supplied by your motion, that is in turn using gas.

I suspect, but again it would take a wind tunnel to verify this, that a bed cap that was the same height as the cab would also reduce wind resistance and improve gas mileage somewhat. However, the added weight of the cap may counter any benefits gained from the reduced drag.

I agree with martinoledad, the gas savings in any case will be pretty small.

- Jack