Sometimes late at night on open quiet hiways when I'm cruising and want to get highest range possible.. one of the buttons I reach for mirror folding. I figure it reduces frontal area a bit and probably helps. (wikipedia) Side mirrors Side mirrors both increase the frontal area of the vehicle and increase the coefficient of drag since they protrude from the side of the vehicle. In order to decrease the impact that side mirrors have on the drag of the vehicle the side mirrors can be replaced with smaller mirrors or mirrors with a different shape. Several concept cars of the 2010s are replacing mirrors with tiny cameras but this option is not common for production cars because most countries require side mirrors.