Interesting blog, but with just one sampling, not scientifically viable. First to be statistically viable, the test has to have a large sampling (not one guy in a truck). They each have to go hundreds of miles, plus all the extraneaus factors have to be removed. For example anyone who pilots an aircraft know that difference in temperature, humidity, wind direction and speed makes for different air densities and affects drag. Did the pickup guy measure these (not only daily but hourly) to create a formula for taking the differences on different days into account?
On the ground there could be different traffic patterns. One day more traffic than the other, or they stop at more lights, or the same factors that affect air density, could affect the tires grip on the road, etc. Was he carrying more in the truck one day than the other. How big a lunch did he eat each day and how much beer did he drink.
Granted the Mythbusters only used one example, though I think they used a track, but when the engineer in the wind tunnel talked about the effects of drag, the consenses was that the tailgate down actually created more drag in the slipstream.
They have used wind tunnel with smoke indicators thousands of times at different labs around the world to look at drag with vehicle design, athelete performance, cyclist positions, even the drag of different swimsuit materials, etc. The more drag, the more energy needed to move...
So theroretically you get better gas mileage with the tailgate up. The question is however, how significant is that savings? A few pennies an hour, a day, a week, a month? Someone someday will either come up with an answer using drag coeficients of wind tunnel patterns, or will drive a whole bunch of identical trucks at an indoor track for thousands of miles.
Nicole, who really enjoys all the links Bob provides the forum and hopes Bob still likes her after this post!