kubel wrote:Mythbusters did an episode on this. They found that leaving your windows down is always the better option when it comes to fuel economy. But they weren't exactly driving vehicles that were heavily dependent on aero-efficiency. As I recall, they were F-150s.
Hmm. My Dad did this same test with his Olds Cutlass and A/C won. He used cruise control (this was his 1st car that had it), filled the tank, drove a couple hundred miles with the windows opened a couple of inches to keep things cool, filled it up again, then drove with A/C. It was on Rt 95 between NJ and MA, so there wasn't too much elevation change, if anything the open windows portion had the advantage as there are more hills in CT & RI. As I remember it A/C won by a couple of mpg. I got that car in college, best mpg I ever got was 23 on the highway and it definitely wasn't as aerodynamic as a LEAF.
I don't have too many controlled chances to test this as the terrain varies too much for my travel, but I'll bet that the additional drag of open windows has more of a load than A/C with closed windows (the A/C load is nothing compared to the heater).