Opel Rak E Concept

There are many unusual things about the BMW i3 Concept electric minicar revealed last month, including its glass doors and roof, not to mention BMW's first production battery-electric powertrain. But the BMW i3 is also at the leading edge of another efficiency trend: tall, narrow tires that reduce the vehicle's wind resistance compared to the usual short, wide tires fitted to cars today. Fitting low-rolling-resistance tires to a line's most efficient models is now de rigeur. Over the years, these harder, lower-friction tires have gone through several generations, so that's today's versions...