Of course smaller and lighter and streamlined vehicles help a lot too, especially with the right engine and technique. I assume everyone has seen the 470mpg deal,
1985 Matsu talks,
http://www.craigvetter.com/pages/470...nomy-main.html . To the two wheeler crowd, the xprize figures are an efficiency joke
Especially given the %25 occupancy rate of vehicles on the road.
also, lighter engine means less energy lost in rpm changes, as well as less reciprocating losses.