What’s the Difference?
The good old mpg that we’re all familiar with measures the distance that a car can travel using a single gallon of gasoline. The numbers we see on window stickers are based on the results of a series of tests designed by the EPA to measure a car’s efficiency in varied driving conditions. MPGe, on the other hand, measures the distance that a car can travel using the same amount of energy as is generated by burning a gallon of gasoline. An EPA formula has calculated that amount at 33.7 kilowatt hours. Many electrified vehicles earn close to – or more than – 100 MPGe, even if they can’t make it 100 miles on a single charge.
Efficiency vs. Range
The key (and somewhat confusing) distinction here is between efficiency and actual electric range. Take, for example, the Chevrolet Volt and the Ford C-Max Energi. The cars have comparable MPGe ratings (the Volt is rated at 98 MPGe combined, while the C-Max is rated at 100 MPGe combined). However, with thirty-eight miles of electric range, the Volt far outreaches the C-Max’s twenty-one miles of electric range. If you have a thirty-mile commute, the Volt can make the whole trip without engaging its gasoline engine, whereas the Energi will have to travel roughly nine miles on engine power. As with everything else, these figures vary with driving style and conditions. Once the C-Max’s gasoline engine takes over, the C-Max earns 43 mpg combined. This means that in the hypothetical thirty-mile commute, the C-Max’s last nine miles would be less efficient and more expensive than the Volt’s, since the Volt would still be chugging along on battery power with 98 MPGe. Because of the wrench that battery range throws into the works, it’s a good idea to consider both MPGe and traditional mpg when looking to buy a plug-in hybrid. Plug-ins receive separate ratings from the EPA for MPGe and mpg. So take your commute into careful consideration. If the commute in this scenario were only fifteen miles instead of thirty, the C-Max would have been the more efficient choice by a nose. Fully electric vehicles will always achieve their highly efficient MPGe numbers, but they also may not take you as far as you want to go, so battery range is still a crucial measure to consider if you make long trips often. Read more about electric and hybrid vehicles here.