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More MPG math:

June 22, 2008

The New York Times’ always-great “Wheels” blog points out that “miles per gallon” perhaps isn’t the best metric, or at least shouldn’t be the only metric, of fuel savings. A higher MPG figure gives the false impression that the savings are proportional to the mileage. Obviously, a higher MPG rating is always better, but as the fuel efficiency increases, the savings start to level off. Their example is that replacing a low-mileage SUV with an average-mileage car makes a much bigger fuel cost difference than trading an average-mileage car for a hybrid car. Let’s do some math and see what that means for scooters.

Of course, this ignores vehicle price, maintenance, taxes, insurance, etc, we’re talking strictly fuel savings. We’re assuming a gas price of $4 per gallon for our example:

  • An 18mpg SUV uses .0556 gallons per mile (22.2¢ per mile)
  • A 28mpg car uses .0357 gallons per mile (13.9¢ per mile)
  • A 54mpg car uses .0185 gallons per mile (7.4¢ per mile)
  • A 60mpg scooter uses .0167 gallons per mile (6.7¢ per mile)
  • A 100 mpg scooter uses .0100 gallons per mile (4¢ per mile)

So if you switch from an 18mpg SUV to a 100mpg scooter (if such a thing exists), you’re saving almost 19¢ a mile. Boo-ya. No-brainer. But switching from a 28mpg car to a 60mpg scooter (a 32mpg difference, saving 7.2¢ a mile), actually saves less per mile than switching from an 18mpg SUV to a 28mpg car (a mere 10mpg difference saving 8.3¢ per mile).

A 100-mpg scooter sounds great, right? Sure, but it’s only saving about 4¢ a mile more than a 54mpg hybrid, not much considering the 46-mpg difference. A hypothetical 200-mpg scooter, awesome as it sounds, would only save an additional 1.67¢.

Obviously, you’re always saving more gas (and more money) with a higher-mpg vehicle, which is good. But your savings decrease as your mileage increases. In the same vein as sunscreen SPF and digital camera megapixels, a higher number is technically better, but after a certain point, the returns diminsh considerably. Just something to consider as you’re measuring your fuel savings or considering a scooter purchase.

Comments

8 Responses to “More MPG math:”

  1. White ApacheNo Gravatar on June 22nd, 2008 4:59pm

    I’m not sure I get the logic of the author. I understand that savings will be more substantial when you begin by idiotically driving a huge SUV and switching to a scooter. But why would one have to drive a huge expensive, gas guzzling car to get the most benefits?

    I switched from a Honda Accord to a Buddy. That seems like a logical move. Yet, the author implies that the savings between a Prius and a Scooter are minimal. That’s ridiculous. A Prius would cost around $35k. That would take forever to make back any savings. My scooter cost $2.5k and gets almost twice the mileage of the Prius. I’m scratching my head trying to figure out how my savings would be only minimal, at at a difference of 4 cents per mile.

  2. Steve WilliamsNo Gravatar on June 22nd, 2008 5:38pm

    Whenever I try to get my head around economics related to the Vespa my brain starts to itch. This is a nice post that has me feeling fine. Until I start thinking about tires, maintenance, original cost….

    Good thing I ride purely for the fun of the thing!

    Steve Williams
    Scooter in the Sticks

  3. bfreedNo Gravatar on June 23rd, 2008 12:11pm

    I’m not sure the target audience of the article is scooter enthusiasts. Anyone can see the glaring omissions if it were an article about buying a hybrid vs. buying a scooter. 1,000% higher initial cost is certainly one, and the author admits that.

    The message I take from it is that the average SUV driver shouldn’t throw up their hands and give up on conservation just because they can’t switch all the way to a scooter (2-wheelers are not a fit for every situation). Choosing a 22mpg truck over a 20mpg truck saves the same fuel as a 100mpg scooter vs. a 70mpg scooter.
    If I were to summarize a main point, it’d be “SUVs are *SO* bad that you can help both your wallet and the environment a huge amount by doing *ANYTHING* else.”

    Fuel savings are only one reason to ride a scooter.

  4. illnoiseNo Gravatar on June 23rd, 2008 12:17pm

    Well, also my point was that once you hit the 60mpg mark (or thereabouts) there’s not really much difference between scooters, and they arguably don’t really save much more than hybrids. All these inflated MPG figures we’re seeing on scooters are all rather pointless because any scooter will give you very substantial fuel savings.

  5. keith_benedictNo Gravatar on June 25th, 2008 1:55pm

    These numbers might seem disturbing when viewed at the micro level (gallons of gas per mile). After all, I’m adding 40MPG (from 60MPG to 100MPG) and I’m only saving 2.7 cents per mile?!? But expand that to a wider view, say one full months worth of gas, and you’re saving $26.60 per month (based on 1000 miles per month). Go even further and expand that to an entire year’s worth of driving and you’re looking at a saving of $320 per year!

    Now, look at this from the most logical scenario (somebody trading in their 28 MPG Accord for a 70 MPG Vespa) and you’re only looking at a 8.6 cents per mile savings. But that 8.6 cents per mile savings equates to a nearly $86 per month savings and a whopping $1,029 per year savings.

    Now add the insurance cost differences (probably $50 or more per month savings) and you’re looking at big dollars.

    I don’t know anybody who wouldn’t mind having an extra $1629 in their pocket every year.

  6. pjchmielNo Gravatar on March 3rd, 2009 10:29am

    I just noticed a typo in the article:
    “switching from a 28mpg car to a 60mpg scooter (a 22mpg difference!)”

    It’s a 32mpg difference, not 22.

    I still think this is a strange article that seems to end up somehow suggesting that people should drive slightly-more efficient cars rather than scooters. A more relevant but usually overlooked aspect is how many people a vehicle is moving for its MPG. An SUV with only the driver vs. a 125cc scooter two-up is a startling contrast in passenger MPG (scooter would be about 500% more efficient), though an SUV with 6 people vs. a low-MPG scooter would come out ahead, overall. A city bus full of passengers, even at less than 10mpg would blow them all away.

    If everyone bought scooters to use instead of taking public transit, bicycling, walking or even carpooling, it would be an environmental disaster. But since most people drive their 2,000+ lb. cars alone, and ride scooters alone, the comparison in MPG is apt.

  7. illnoiseNo Gravatar on March 3rd, 2009 10:51am

    Typo is fixed, thanks, PJ.

    As to the rest of it:

    I’ve pointed out the passenger argument many times in other posts, and of course if varies by situation. In your example, yes, of course a 2-up scooter vs. a 1-up SUV is a huge difference, but it’s shocking how many people I’ve met who try to defend purchasing A PAIR of scooters as being fuel-efficient, the difference between a pair of scooters and a fuel-efficient small car (in footprint, economically, and environmentally) is negligible, and in many cases the car would come out ahead, with the added benefit of being safer, more comfortable, and able to carry groceries and kids.

    And again, I think you and others are missing the gist of this article entirely. If you’re looking to save money on gas, high fuel efficiency is obviously better. But what people don’t realize is that you get diminishing returns, and your savings per mile become smaller and smaller (though there’s still always a savings) the higher the fuel efficiency. That jump from 18 to 28, for instance, is way more productive, economically, and the jump from 68 to 78 mpg is fairly minimal, economically. The point is, the shift from SUV to hybrid is a more realistic and productive goal for most Americans. If they can go that extra step to a scooter, that’s great, but it’s not making as much of a difference as they may think.

    Moreover, in the big picture, a 10 or 15mpg upward shift in the average american car efficiency could make a much bigger environmental and economic impact than the scooter MPG wars, even if the number of scooterists in America tripled over the next year.

    Of course cycling or walking or public transportation beats it all. And a lot of scooterists trying to justify their scooters with economics or ecology would have done a lot better to buy a bicycle, or an electric bicycle, or switched to public transportation or carpooling. And it would have cost them far less.

    In a vacuum, this story is sort of flippant and depressing, yes, but it seemed important to dispel some of the ridiculous marketing and hyperbole that was used to market scooters last year.

  8. orinoNo Gravatar on February 26th, 2012 2:34pm

    A buddy of mine did the sums about a year ago and discovered his Scion xB costs way less per mile to run than his Vespa GTS. Of course, the scooter gets way better gas mileage, but on the downside it needs a new rear tire about every 4000 miles, and generally requires much more frequent service, which is more expensive per visit if you have it done at a dealer (he’s able to do oil changes and other minor stuff himself).

    But you’re right, on a purely economic basis, a scooter doesn’t make a whole lot of sense. Stuff like free or reduced parking costs, and the scooter’s smaller form factor, would be stronger justifications than gas mileage or carbon footprint…

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