I detailed some half-bed tonneau plans in a previous post. I filled up last night and calculated the mileage and it came out at 17.7, which isn't too encouraging. I had already run 100 miles without the tonneau though, so only 2/3 of the total mileage would have been affected. Also, I was unable to run a lot of highway miles, where I'd really feel the wind resistance and benefit from a lower Cd value.
Since I'm now driving around with a big chunk of plywood covering part of my bed, Michelle's been pretty embarrassed. Admittedly, it's a deep-south look, the kind of thing you'd expect to see in Marianna (smack!). But under the redneck facade of the plywood is deep, earth-shattering science.
Trying to avoid small trips with this tank to get a better reading. Might add the F-150 to Green Hybrid to track it easier. Especially if I can get the 21-22 MPG I think this mod is worth (hwy obviously)