Reverse your Car Logic!

Posted on August 4, 2010. Filed under: News | Tags: , , , , , , |

Last week’s unveiling of the Chevy Volt brought automobile efficiency to the forefront of public discourse.  The long awaited release of the Volt was somewhat of a disappointment, as critics slammed its high sticker price and limited range (40 miles on pure electric charge).  But its mere presence is still a big step forward for greening the auto industry.

Indeed, images of the environmental disaster along the Gulf Coast and creeping gasoline prices are causing many re-consider a “green” auto purchase – of either a hybrid or new electric vehicle.  But before you hop on the Prius, Volt, or Leaf bandwagon, consider the real efficiency gains gleaned from trading in your conventional car with a more efficient one.

Growing up in the United States, we have come to embrace the MPG rating slapped on new car windows.  Gas guzzling SUV’s have MPG ratings of 15 or lower, while the relatively efficient Civic is rated near 30 (combined).  However, we may be looking at auto efficiency from an entirely wrong angle.  Rating a car on “miles per gallon” can be quite misleading.  Comparing fuel consumed per unit of distance and not distance per unit of fuel consumed is a much easier (and more accurate) concept.  If I just lost you, I’ll break this down.

If we measure by gallons per mile instead of miles per gallon, we would be able to gather exactly how efficient our cars are.  For example, what is better?  Replacing an 18-MPG car with a 28-MPG one, or replacing a 34-MPG car with a 50-MPG one?  A quick calculation would tell me that 18 to 28 is only 10, while 34 to 50 is 16.  But if we express these comparisons as gallons per 100miles, we find that an 18-MPG car consumes 5.5 gallons/100miles while a 28-MPG car consumes 3.6 gallons/100miles (a saving of 1.9 gallons.  If you trade in your 34-MPG car with a 50-MPG car, you’d find that the 34-MPG car consumes 2.9 gallons/100miles while the 50-MPG car consumes 2 gallons/100miles (a saving of only .9 gallons!).

Measuring cars in gallons per mile shows that there is a law of diminishing returns when it comes to ever increasing MPG ratings on cars.  Basically, it is much more effective to trade is very low mileage vehicles for higher mileage ones rather than trading in already high mileage cars for even higher mileage ones.

Not that I am against trading in your Civic for a Volt, but think twice before making your purchase, and don’t forget to reverse your car logic!

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