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Though this is an old thread, this is always a topic of interest.

Where both the linked Mythbusters and the SEMA tests fail is they cause people to incorrectly correlate that if it's true for one pickup, then it's the same for all pickups. Various pickup designs are aerodynamically different so these results are not comparable.

For instance, the quad cab mentioned earlier in the thread will have a different airflow pattern over the bed, as will fleetsides and stepsides. The SEMA article is especially flawed in that the pickup was tested with the side mirrors removed. These non-real world conditions provide irrelevant results since the airflow will be less turbulent and flow differently over the bed than a more disturbed airflow.

For reference, here's a link to Consumer Reports comparison test of tailgate up and down, and bed cover http://www.consumerreports.org/cro/news/2013/08/pickup-truck-tailgates-and-fuel-economy/index.htm

This testing is done under real world conditions so it's also inexact, but much closer to what we'll encounter. An aspect that's rarely mentioned in the highly vaunted wind tunnel test results is the effect of sidewinds, which are almost never tested. So while headwinds are the primary factor in driving, we must remember wind tunnels don't account for off-center and sidewinds, turbulence from other vehicles, and tailwinds.

In my experience, my best mileage is achieved with a bed top (camper top) despite the extra weight. I speculate this is due to it approximating a Kammback profile.
 

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Though this is an old thread, this is always a topic of interest.

Where both the linked Mythbusters and the SEMA tests fail is they cause people to incorrectly correlate that if it's true for one pickup, then it's the same for all pickups. Various pickup designs are aerodynamically different so these results are not comparable.

For instance, the quad cab mentioned earlier in the thread will have a different airflow pattern over the bed, as will fleetsides and stepsides. The SEMA article is especially flawed in that the pickup was tested with the side mirrors removed. These non-real world conditions provide irrelevant results since the airflow will be less turbulent and flow differently over the bed than a more disturbed airflow.

For reference, here's a link to Consumer Reports comparison test of tailgate up and down, and bed cover http://www.consumerreports.org/cro/news/2013/08/pickup-truck-tailgates-and-fuel-economy/index.htm

This testing is done under real world conditions so it's also inexact, but much closer to what we'll encounter. An aspect that's rarely mentioned in the highly vaunted wind tunnel test results is the effect of sidewinds, which are almost never tested. So while headwinds are the primary factor in driving, we must remember wind tunnels don't account for off-center and sidewinds, turbulence from other vehicles, and tailwinds.

In my experience, my best mileage is achieved with a bed top (camper top) despite the extra weight. I speculate this is due to it approximating a Kammback profile.
 

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I like towing with my canopy on. Seems to be less wind resistance and sway. I drive to Texas from Washington and it drove better. Now the canopy is off because it wont fit in my garage. the trailers seem to buffeet more going down the road.
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