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In January 2007, SEMA’s Market Research Department conducted a study to test the affect tonneau covers have on the coefficient of drag for pickups. Four trucks were tested: a 2006 Ford F-150 with a 5' 5" bed; a 2005 Ford F-150 with a 6' 5" bed; a 2006 Dodge Ram 1500 with a 6' 5" bed; and a 2007 GMC Sierra with a 6' 5" bed. These trucks were tested at the A2 Wind Tunnel in Mooresville, North Carolina, with 13 different tonneaus from nine different manufacturers.  

Rising gas prices are not only a concern for consumers, but also for truck manufacturers and anyone who manufactures aftermarket parts for pickups. If consumers decide not to buy pickups because of their gas-mileage ratings, a lot in the industry suffer. If consumers see that the addition of a tonneau cover could improve fuel economy, they may continue to buy pickup trucks at the rate they always have. After all, a truck enthusiast would much rather drive a pickup than downsize to a subcompact.

The wind tunnel test produced great results.  All 13 products tested improved the coefficient of drag, Cd, by at least 4.2%.  The improvements ranged anywhere from 4.2%–7.8%. Other tests would need to be conducted in order for fuel economy to be calculated, but it is safe to say that a reduction in drag would improve fuel efficiency for these pickups.

Six products were tested on the 2005 F-150.  Cd was normalized to 1 for all pickups. This was done in the interest of both the truck manufacturers and the tonneau cover manufacturers.  This also makes it easier to report percentage decreases in Cd. The following chart shows the results.  You will notice the baseline Cd value for the truck is represented by the blue dot at 1.  (Baseline values were calculated for the trucks at a wind speed of 85 mph, with no tonneau installed, tailgate in upright position)  You will also see the values for the test with the tailgate down.  As you will notice, lowering the tailgate has little effect on Cd.  

OK, so the drag coefficient was reduced, but only by an average of 4%. I highly doubt this results in much actual fuel savings. The force of drag on a vehicle isn't significant if the vehicle isn't traveling at 40mph+, and even then it's not truly powerful until about 55-60 mph.

SEMA is the industry organization for companies making vehicle accessories...no wonder they're touting the benefits of tonneau covers.

BOGUS!  
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