Droptail® is an exciting microprocessor controlled bolt-on system that automatically deploys the tailgate into a spoiler position, for best aerodynamics at drag-inducing highway speeds, to improve mileage and performance. At speeds above 50 MPH the tailgate automatically opens to 50°, then closes again below 30 MPH. Alternately, any tailgate operation may be accomplished through the use of a remote control. Tailgate theft is prevented ,as an RF-remote is required to open the gate and gain hardware access. Rear backup visibility, particularly desired when children are present, can be significantly improved by in-cab manual deployment of gate. The system also enables hands free access to the cargo bed and eliminates having to lift a heavy gate. Fits all F150 - SuperCrew & SuperCab with 8' bed require additional wiring harness to lengthen wires. Subject to stock on hand, no backorders.

 

 

I don't have a source, however it's not unbelievable that the position of tailgate effects different cars differently.

Although I'd think that mostly means differences between older, less aerodynamic trucks, and newer ones where wind tunnel testing were part of the design.

 

There was a very authoritative physics study done by the U of Michigan ( I think ) that conducted wind tunnel test for drag coeficients etc. This topic has been posted here in the past and when it was I posted the correct info about the study. I cant remember all the who and whats now but the bottom line was that your drag is less with the tail gate up because of a circulation air bubble that forms in the truck bed and helps to reduce or smooth the drag profile at he back of the cab. With the gate down the bubble doesnt form and the suction or drag on the cab and rear end of the truck is greater. From what i remember the milage difference was only 0.2-0.3 mpg.