So, how much MPG do you think I am loosing realworld having a roof rack on a minivan? I have a 96 Windstar, and I know I am never going to get great millage, but Im hopping to get a little more to a tank. Wondering how much I would gain[if any] for loosing the roof rack?
You'll note that the new GM 2-mode hybrid SUV's come without roof racks for a reason.
I measured (unscientifically) a 12.7% hit with old-skool racks on my Firefly. That's with them empty.
General estimates are hard to come by (precisely because the situation will be different for different vehicle/rack designs). I've seen them range from 5-20%. I'd say (WAG) the Windstar's closer to the bottom end though, based on their design.
But as with all questions aero, it depends on how much highway driving you typically do, and how fast you go when you're there.