sikbrik - most people here would agree it's good to ask questions like that, with an open mind. I'm tempted to reply to your question with a question:
How many of the highest-efficiency vehicles or prototypes can you name that have roof rack side rails?
It's generally understood that roof racks (and side rails on their own) increase both frontal area and drag coefficient. (Consider also that we more often drive in cross-winds than we drive in no-wind/headwind/tailwind situations, where side rails will have a bigger impact than might be thought at first.)
OK, sure - most high-efficiency vehicles are "econoboxes", not designed with racks/rails in mind.
So what if we look at some higher-efficiency non-econoboxes? EG: Toyota engineers deleted the racks/rails from its RAV4 EV, specifically to improve efficiency (
http://ecomodder.com/forum/showthrea...-ev-23146.html) . As did GM with its full-size hybrid SUV's. Just 2 examples off the top of my head - there are probably more.
I wouldn't be surprised if someone could come up with an unusual design where side rails somehow helped, but I think it's pretty unlikely that design is on the road.