Log in   •   Sign up   •   Subscribe  feed icon

GM Rates Volt at 230 mpg: Outrageous Claim or Realistic Number?

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.

George Delozier
Motorized Innovations

Aug 22, 2009
by Anonymous


Who works 50 miles away?! That would take them like 2 hours to get to work!

Aug 22, 2009
by Anonymous


Why do standards bodies insist on giving us derivatives when they could simply present the raw numbers which are indisputable and testable and repeatable.

For a hybrid vehicle I would want to know
1. Total mass
2. Total drag
3. Fuel capacity
4. KWH battery capacity
5. miles per KWH running pure electric
6. miles per gallon with engine running constantly to keep batteries topped off

Then you'd have a phone app that would estimate mileage and suggest best recharging schedule based on detailed trip planning. It would work for any car or truck given the above 6 datums.

We live in an innumerate society. Too many fell asleep in high school physics class because they had already fallen asleep in math.

Insisting on undefined derivative numbers is a sign that this society assumes innumeracy and assume you cannot perform a simple algebraic operation. With expectations so lowered, it is a self-fulfilling prophecy, reinforcing innumeracy and bringing the society down to the lowest common denominator; innumeracy and its inevitable corollary, inability to exercise precise critical thinking.

Aug 22, 2009
by Anonymous

The article incorrectly

The article incorrectly compares electricity price to gasoline price to arrive at an estimated mileage of 300 mpg.

The EPA formula GM used compares CO2 emissions of electric power generation from a plant vs CO2 emissions of burning gasoline in your car. It assumes that energy from a plant is generated about 2.5x more efficiently than burning it in your car with respect to CO2 (plant about 40% efficient vs car about %15 efficient).

So the 230 mpg tells you how efficient the car is with respect to CO2 emissions. Not price or energy efficiency.

Price per mile doesn't make sense because everyone has different energy prices.

Energy per mile makes sense. If you remove the ~2.5x bonus from electric power it would bring the mpg equivalent in line with other electrics around 100 mpg equivalent.

Aug 22, 2009
by Anonymous

battery life

50 year old cars are still working. not great but still work. in electric cars the big problem is battery life. in laptops its 3 years, the government has to mandate a battery exchange program available at every gas station. a monthly fee gets you unlimited battery exchanges. you give them your empty battery they give you a fully charged one.

Aug 22, 2009
by Anonymous

wake up 'bro'

One day you may wake up and realize that it is not the Chevy Volt that is plugged in, but you are instead plugged in. You are not plugged into a source of power; you are plugged into lies. After people have wasted enough money purchasing GM products, the scam will burn out. Then the next gimmic to waylay the hapless will be developed. The cycle continues in this way. Purchase the product, realize that you have squandered money, then wait for the next piece of crap to come down the chute. You learned lies in physics and math class as well. This vehicle is just another GM product that will break down, have recalls, and consume more fuel than import vehicles in its class. Do you work for GM?

Aug 23, 2009
by Anonymous

50 miles from work

I live in a quiet rural setting and drive 50 miles to work - this takes me about one hour each way and then I work a 10hr day, four days a week. Little tough but with my audio books, it works.

Aug 23, 2009
by Anonymous

You are dilusional

And an idiot.
Lies in physics and math??? Really?
BTW my Corvette is the best car I've ever purchased.

Sep 21, 2009
by Anonymous

GM(America)'s Volt

GM(China) will rear its ugly head at the politically appropriate moment and flood America with a BYD - like car, with a proven run in Shanghai China in taxi service. This will happen at the perfect marketing moment, and for the largest mark-up on any car sold in America, and it will be, compared to the "Volt" a real winner! Right now as we speak, GM(China) has docks full of Shanghai Buicks and Cherry's just waiting for export conditions to be right for the American and European markets, but you must understand, profits are now measured in "Yuan", with communist government aspirations, a very different situation, different legal setup, so normal "American" capitalist equations, theories, means of control and extortion, no longer are valid, only those used by China's and Asia's intelligentsia, so we are also out of the speculative picture! We have become "Third World" consumers in a very short time, and must go through appropriate attitude adjustments as well! One folly easy to see, GM(American) still uses 1930's "Yardsticks" and measures "Efficiency" in "Miles per Gallon" , engine outputs in "Horse-Power" not Kw. Everyone else looks to liters per 100 kilometers, and for Electrics, the total distance traveled on one charge! Perhaps this 'Lead headdedness" or the Prozac in the drinking water in Michigan from Shiite-ing in their drinking waters instead of bio-digesting like civilized folk the world over, has finally gotten to the management that publicized this monumental blunder. I feel sorry for them, even the Hyundai folks knew better.