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[edit]
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.[10][11] 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[12] but this option is not common for production cars because most countries require side mirrors.
(wikipedia) Side mirrors[edit]
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.[10][11] 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[12] but this option is not common for production cars because most countries require side mirrors.