Max:
I am on my second iteration of air dam. The first one extended to within 1.5” of grade and got the 27.00 by itself. I also had side skirts where the running boards used to be. They approached 3” of the ground. Air dam & skirts that low dragged the ground a lot. No damage due to the fact they were ripstop conveyor belting but an annoyance all the same. With the air dam that low I probably lost some CdA due to increased frontal area.
Second iteration, I ditched the side skirts (more trouble than they were worth) and raised my air dam up to 6” above grade in front of the wheels and 9” above grade in the center (just covering the steering tie rod). MPG drifted back into the mid 26s. This setup obviously never drags or fouls parking curbs. It passes over most road kill.
Gonna try again, splitting the difference. Probably 3.5” in front of the wheels and 6” in the center.
Homesplat:
I’ll tell you what everyone else around here will tell you. The first order of business is to adjust the nut behind the wheel. (that would be you). Driving style matters – a lot. Read this:
Beating the EPA - The Why’s and How to Hypermile - CleanMPG Forums
Winnow through the politics and the hybrid-only stuff. He has the goods. This advice flat-out works. Few people can drive the way he does but every little thing helps.
As you get into it, everybody and his dog will be trying to sell you some snake oil or gadget for better MPG. Hold onto your wallet. Three things I’ve found to work (once you get your driving improved): Weight reduction (tough on a truck whose whole purpose is hauling cargo), gearing, and aerodynamics. Tuning is a waste of your money (Exception: Ford is notorious for reflashing you ECM for NOx reduction. Such reflashes are highly detrimental to MPG. A chip will trump the reflash.)
How gung-ho are you about mods? I know for a fact that an F-150 with a stick and a Cummins 4BT3.9 will get over 32 MPG – with extensive aero-mods. For cheap and effective (but bizarre-looking) aero-mods, check out aerohead’s trucks. He gets crazy MPG without any mechanical mods.
PM me when you can.