Aerodynamic effects of roof rails: When compared with cruise control set at 65 mph, adding the cross rails of a roof rack (and driving with cruise control set at 65 mph) caused a 1 percent loss in fuel economy from 27.2 mpg (without cross rails) to 27 mpg.

Do crossbars reduce mpg?

Roof rails will not effect MPG, cross bars may to some degree and mostly is not only while traveling at a freeway speeds. If most of your driving is freeway and you're worried about 2mpg then take the cross bars off when not in use.

How much does a roof rack decrease gas mileage?

BERKELEY, California — Automobile roof racks can reduce fuel economy by as much as 25 percent, according to a new study from Berkeley Lab.