On the PBS evening news program was a fifteen minute segment on the top contender for the automotive X-car which gets 110 miles per gallon on E85. The X-prize is 10 million dollars (good incentive).
That contender is the Edison 2 Very Light car http://www.edison2.com/very-light-car
Part of the discussion was their decision not to use batteries and to concentrate on light weight and aerodynamics and the mass of the battery posed a big cost when it comes to acceleration and the need to make components heavier to compensate for the weight adding more weight.
In the design you see the race car heritage and design relies on such components as the wheels as part of the crash worthiness.
This harkens back to a number of threads on using light weight materials aluminum and composite,s as well as aerodynamics. In those threads discussing gas mileage costs I would hazard most information comes from trips of some distance with sustained speeds where weight is not a large factor in stop and go or mountains.
With the exception of the fiber-glassed cardboard or plastic soffet trailers I will again say most teardrops are grossly over engineered battleships.
The car is a four passenger will do 100mph and they hope to sell them for about 16,000$, made entirely in the US.