The only case I've seen where the mileage went up over stock was when HHOTDI moved his roof rack from the roof to a trailer-hitch mount.
http://ecomodder.com/forum/showthrea...tml#post390588
Quote:
Beetle w/o any attachments/slick top= ave 48mpg :{)
Beetle with factory VW Roof racks and CVT tent= 38mpg :/
Beetle with new areo-hitch mounted rack/CVT tent= 49.3MPG
|
A 10mpg hit turned to a 1.3mpg gain. In his case something about the size of your trailer bed was placed high in the natural wake of the New Beetle body.
Flat sides and square corners are sub-optimal. A rowboat turned upside down and back to front would streamline it best.