Tonneau cover and mpg

[22MJ]

Even in something as unaerodynamic as a jeep, the engineers have done every little thing they can to improve mpg straight out of the box. even on trucks. One of the big changes is how wide the top edge of the tailgate is. They used to be very narrow. if you look at say a 90's truck, the very top of the tailgate is an inch or two wide at most. If you look at a modern truck, especially a full size, the center of the top edge of the gate is usually close to 6" wide. That's not for looks, and while in the case of a Ford it does serve to house the hidden step, that's not the main purpose. It's main purpose is to give the air coming off the roof a "landing spot" as a way to smooth the airflow coming off the roof.
Another factor is it basically it comes down to the fact that the bed is too short for it to really matter. on the vast majority of 5 or 6 foot beds this is usually the case. A member of an eco-modder forum did some tonneau cover vs open bed vs tailgate up/down testing and determined that somewhere between 6 and 7 feet is the area where a tonneau cover begins to play a role in aerodynamics. And in those tests on an 8 ft bed, he found that simply adding a small cover over the last 3 feet or so of the truck bed was enough to improve the aero, and contrary to what you may think, air did not get under the cover enough to change results. So it didn't act like a parachute as you would expect.

As for the Gladiator specifically, especially a soft top, the air coming off the flappy material is already going to be so disturbed there's not going to be much you can do to help anyway. and if the top is down, well forget it.

And here I thought tailgate lips were wider as an element of style and to create a waterproof seal with a tonneau cover

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[Fundamental Jeepster]

I went with one to keep moisture and debris out. Plus, I like the cleaner look a cover gives.