Reply #73: I get 27 mpg on the highway in my GM full-size [View All]

It seats six, is quite comfortable, and could probably fit the SmartCar in it's trunk. And it's 19 years old with 183,000 miles on it. And I drive fast.

Fuel economy hits the point of diminishing returns once you get to about the size of a Ford Focus or Chevy Cobalt. Any measurable increase in fuel economy only comes from drastic size and weight cuts, assuming gasoline engines.

Highway fuel mileage is mostly determined by frontal area and coefficient of drag. Since passenger vehicles need to be a minimum height and width, there's not a lot of play in this area. And the C_d of cars at their best is about 0.27. IIRC, the original 1986 Ford Taurus had one of .32, so that's hitting the point of diminishing returns as well.