Earlier this month, GM released information that the upcoming Chevy Volt would be able to see as high as 230 miles per gallon of fuel. Ever more impressive is that the EPA is backing this claim...for now anyway. But the real question is: How did we reach this number to begin with?
First off, it should be noted that the Chevy Volt could get an infinite number of miles per gallon, in theory, if the driver never went on a trip that totaled more than 40 miles. The 40 mile figure was decided upon due to a study that concluded a majority of commuters lived within 40 miles of their place of work. Therefore, assuming they had somewhere to plug in during the day, a Volt owner would be able to travel back and forth without ever using the onboard gasoline engine.
So let's say you decided to live a little farther from work. From your driveway to your parking spot is 50 miles. The first 40 miles are traveled solely on battery power, with the last 10 being made up by the gasoline engine which gets about 50 miles per gallon. While this number is nothing to sneeze at, it is a far cry from the published 230. Once again we ask: Where did this come from?
The problem with offering an fuel mileage rating on a vehicle that doesn't burn fuel all the time is that no matter how accurately you measure consumption during time when it is burning fuel, the average will be skewed by the times when it isn't. This is where that huge figure now associated with the Volt came from.
For example, GM has said that it takes about 8 kilowatt-hours to recharge the Volt from completely drained. Let's also assume you are paying the same $0.40 to recharge the Volt that GM has quoted. So in essence you will have paid $0.40 to go your 40 miles. How does this equate to a normal fuel burning vehicle?
Once again, let us assume the average cost of fuel in about $3.00 (I wish.) The $0.40 you paid for 8 kilowatt-hours would buy you roughly 0.133 gallons of fuel. This is where the line between black and white begins to blur. Many people will now assume that it takes the equivalent of .133 gallons of fuel to go those 40 miles. If you recalculate to solve for a full 1 gallon, you would suddenly be getting the equivalent of 300 miles per gallon!
To combat this problem, the EPA is working on establishing methods to test the actual fuel mileage equivalent of vehicles that use both electricity and fuel to run. The current thinking is to take a fully fueled and fully charged vehicle out for a road trip and see just how far it can really go.
Jumping back to the Volt dilemma, if we follow this method of testing and take the 360 mile range proposed by GM alongside the current fuel tank estimate of 7.2 gallons, we should be able to get a more realistic picture of the fuel economy. By adding in the 40 miles from the batteries and dividing by the 7.2 gallons, we arrive at about 55.5 miles per gallon. This is not to say 55.5 mpg is a bad number, but it is still not the 230 released by GM.