Originally Posted by GXP Venom
Ya, when you move forward, the wind over the cab isn't really disrupted by the box. Covered or not, tailgate up or down, trucks have a blunt front end and little slant to windshield. the wind is still on an upward travel as it goes by the box. I have a heavy topper for my Ram3500 thats even with the roofline. Makes it looks like a dually version of the Ramcharger. I always figured I would get better mileage with it on. When I actually checked, it got worse mileage with the topper on. I assume because of it'* weight.
Our "other" car is the wife'* Prius. It gets 50/52 MPG off highway where the hybrid system can work, 44 MPG on the highway. No mods, LOL. But I have been thinking of how much better MPG I could get with an additional battery from a wrecked one fitted into the spare tire area would bring. The system brings the one to a full charge easily in our hilly area, and I bet additional storage would give some appreciable better MPG'*.
This has actually been proven to have an effect MPG. With the tailgate up a "bubble" forms that allows "new" air to pass right over and increses mileage. With the tailgate down there is no "bubble" so the air goes over the cab, then down into the bed and creates force and drag. That reduces mileage.