just an update, I've had the rack on for a couple of tanks of gas an no noticeable drop in mileage. i usually get 20 to 22 and I got 20.5 on my last tank. I think the vehicle is inefficient anyway and there isn't enough wind resistance to make a difference. now if it would warm up I could report on driving with a bike on top, but I have not done that yet. I now carry a milk crate to stand on to put a bike up there though,