Hold on a second…there’s a problem with the impressive claim made by Chevrolet last week of 230 miles per gallon for its electric Volt model (which is still under development). Actually, two problems.

The first is how to measure the miles per gallon of an electric car. As has been noted in a number of other blogs such as EcoGeek and Good Math, Bad Math, using mpg for electric cars is “far from ideal” (remember — the Volt still uses electricity from coal-fired power stations to recharge its battery).

There’s also the the troubling assumption that, for the first 40 miles after a charge, the Volt doesn’t use any gas — and so gets an infinite mpg! Kinda silly. A true estimate of mpg for the Volt is probably around 100 mpg (which is highly dependent on the length of your commute and whether you can be bothered to plug it in every night).

But even at 100 mpg, should we be SO impressed? And if not, why? That gets to my second problem – the measurement of car mileage itself. And this issue  goes for all cars – normal, hybrid and electric.

Basically, the U.S. auto industry (and those who regulate it) are using a misleading measure of fuel efficiency. Instead of miles per gallon, we should be using the more logical gallons per (10,000) miles. (The rest of the world measures fuel efficiency this way, although generally in liters per x number of miles.)

Why? It’s really simple: For every apparent “doubling” in mpg, you are really only using half the amount of gas. Although this is still impressive, let’s not get sucked into believing the extravagant hype. I will use examples to illustrate the misleading part:

  • At 12.5 mpg (in your great-big-huge SUV) you will use 800 gallons to go 10,000 miles (and incur the wrath of tree-huggers);
  • At 25 mpg (a friendly sedan) you will use 400 gallons to go the same distance; and
  • At 50 mpg (a super-green eco-loving hybrid) you will use 200 gallons.

See the problem? While mpg has doubled each time, it’s the INCREMENTAL SAVING (sorry for shouting) of actual gallons that we should be paying attention to!

While 200+ mpg is impressive (50 gallons per 10,000 miles), the REAL SAVINGS (yes, more shouting) are at the lower end of mpg — in other words, getting the great-big-huge gas-guzzlers off the roads. This is because a vehicle that does 12.5 mpg versus 25 mpg saves 400 gallons of gas! While going from 25 to 50 mpg (“doubling”) only saves 200 gallons. To get even close to that original 400 gallons saving, we would have to go from 25 to 800 mpg!! (387.5 gallons of saving.) See?

So, with SUVs averaging 18 mpg (versus 24 mpg for regular cars), it’s much more important to get the 99 million SUVs and pick-ups off U.S. roads (or drastically increase their fuel efficiency) than it is to pour all this effort into producing super-high-fuel-efficient cars (that in reality barely sell in comparison to SUVs).

(Image: Chevy Volt. Credit: jurvetson through a Creative Commons license.)

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  1. This is an interesting observation regarding gallons per mile. It goes to show the diminishing returns in terms of saved petrol as cars get better mpg.

    I’ve also put some more stuff about GM’s ludicrous claims on my blog at http://aphanez.blogspot.com

    Feel free to comment on any errors in my analysis.

  2. Don’t forget, Electricity cost money. In my neigborhood electricity is .15 for KWH. If Chevy Volt needs 8 KWH to do 40 miles, that means it only gets the equivalent of 88 MPG for the electric miles.

  3. I’ve seen you post about this before. I would just like to point out that actually, the EPA does almost exactly what you describe, albeit multiplied by one extra number. Each car has not only the estimated MPG (highway, city, and estimated combined), but it also (in smaller print) estimates the annual fuel cost for each vehicle. This is basically what you’re advocating (gallons per annual mileage, which is estimated at 12000), multiplied by some average fuel cost. At any rate, it is still proportional to the ratio you are advocating, and can be used to compare the savings in cost (and thus, in gasoline usage) as a result of an increase in MPG.

    I would be more worried about the fact that apparently some people can’t take the inverse of the ratio and figure out what it means, even with a calculator…

  4. The important question: are Americans more concerned with saving money or saving gas?

    There’s no doubt that buying a more economical car will save more gas, but will it also save you money? Would driving your paid off SUV actually be cheaper than driving a new hybrid?

    The car payment on your SUV is $0.
    If we use 800 gallons of gas per year @ $2.50/gal = $2000/yr
    Let’s say insurance is $50/month $600/yr
    Let’s even throw in some repairs for an older, out of warranty car – $50/month $600/yr
    Total = $3200/yr

    Car payment on a hybrid, maybe $300/month or $3600/yr for 5 years
    Gas at 200 gallons a year @ $2.50 gallon = $500/yr
    Insurance is going to be higher since you are financing, let’s say $75/month $900/yr
    Total = $5000/yr

    So you save $1800/year or $9000/5 years driving your 12.5 mpg SUV over a hybrid. Weird huh?

    Even if you decided to buy a $5000 SUV that got 12.5 mpg, you’d still come out ahead of the hybrid.

    What does all this mean? You can be green and spend the extra money on financing a hybrid, or you can be un-green and pollute more in your SUV, but save a decent amount of money.

  5. Don’t kill the electric car again! It should have been around for 20 years by now.

    Decreasing our dependency on oil is a GREAT thing.

    Using Solar power to lessen our dependency on coal is another advancement that needs to be further made available to the public.

    The guy from GM was simply saying that you can go 40 miles on a charge, then you can go another 190 with the tank on board that aids in electric production. Like he said, the average American drives less than 40 miles back and forth to work. I drive 46, so it would cost me less than a gallon of gas a day to drive back and forth. Now, if companies would then install a solar recharging station for each parking lot, everyone could recharge at work and keep the green theme going.

    Have some patience with this everyone. It is for the best.

  6. The battery has a larger carbon footprint than a ford focus before it rolls off the assembly line. Mined in Canada refined in Europe and manufactured in China. Now they are saying a Volt will need 2 sets of batteries before the warranty is thru. $10.000 per. Buy 2 Ford focus. It’s greener with gas.

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