You may know about MPG. But do you know your gallons per mile?
Back in June, we took a look at the distinction between miles per gallon (MPG) and gallons per mile (GPM). At first blush, it may seem this is a six of one, half-dozen of another situation. It's not. MPG is the most common number cited when people want to understand how efficient a car is, especially in the US. Richard Larrick, Associate Professor of Management and Organizations at Duke University, says that the MPG number is wholly inadequate to understand the way that car models get cleaner through the years. Larrick and his team are totally in favor of cars with higher MPG ratings, but just want to make sure that everyone understands that - purely in terms of how much fuel is burned over 10,000 miles - a jump from 10 MPG to 11 MPG gives the same savings as going from 33 MPG to 50 MPG. In each case, you'rve reduced your consumption by about 100 gallons.
To help understand GPM, Larrick has put up the MPG Illusion Calculator on his MPG Illusion website. The Calculator uses the mileage data from the EPA we're all familar with, but presents it in such a way that you get to see how many gallons it takes to drive a set distance. So, for example, I punched in a comparison of the Prius (46 mpg) and the Civic hybrid (42 mpg). If you drove each vehicle 1,000 miles, how much more gas would you use in the Civic? Go ahead and guess. The Calculator says it's just two gallons. You can also use the flash-based tool to compare all 2009 models sold in the US.
Larrich wrote to AutoblogGreen that, "These calculations are critical to helping people see their true gas consumption (and carbon emissions) and not be tricked by MPG. I'm eager to see either the EPA or Consumer Reports adopt GPM, and am trying to provide the necessary tools in the meantime." What's your GPM?
[Source: MPG Illusion]
Reader Comments (Page 1 of 3)
!!D 8:38PM (12/16/2008)
Illusion? Only for people who are bad at simple fractions.
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Treplaw 9:39PM (12/16/2008)
Which is a startlingly large percentage of people. And not everyone stops to really consider the math, for most people 1 mpg is one mpg weather it is from 10 to 11 or 33 to 34. It is a reasonable concern.
axioll 4:32AM (12/17/2008)
!!D, there's definitely an illusion here, however its their argument.
--"Truth is not the absence of propaganda; propaganda thrives in presenting different kinds of truth, including half truths, incomplete truths, limited truths, out of context truths. Modern propaganda is most effective when it presents information as accurately as possible."
In other words, effective propaganda uses accurate information - selectively - to portray a perspective or argument that is factually out of context and not truthful. This article does just that. Yes, the math is accurate, however the insinuation that jumping from 10 to 11mpg (saving 100gallons) is equivalent to going from 33 to 50mpg (because you also save 100gallons) is blatant deception. Gallons saved does not equal dollars saved. Contrary to the distortion this comparison presents, the 11mpg car costs substantially more ($1,820) versus either the 33mpg ($610) or 50mpg car ($400) over the same 10k miles; and you will still save more $$$ on the 33-50mpg jump ($210) versus $180 for the 10-11mpg jump.
--"Propaganda is not so much designed to change opinions so much as reinforce existing opinions, prejudices, attitudes. The most successful propaganda will lead people to action or inaction through reinforcement of what people already believe to be true."
If one read Sebastian Blanco's write-up and its accepted its suggestions at face value, they would walk away thinking "So I can trade in my 10mpg SUV for another one that gets just mpg better...Its like I'm upgrading from a 33mpg ride to a 50mpg Pruis...but I get to keep my SUV woopee!" In this case their *prejudice* toward favoring lower mpg models - and *attitude* that those high mpg figures are all fuzzy math (because you save the same # of gallons anyway?!) - would be *reinforced*. The propaganda has effectively guided them toward a state of inaction, by lulling them into a false sense of security in staying with low efficiency models.
This type of propaganda has been a reoccurring meme here: that higher mpg figures are meaningless, and the higher the mpg the more meaningless it is. Meanwhile these same "writers" put out pieces nudging people to buy premium gas, because you know its so much more efficient to buy premium, rather than say, actually getting a car with better mileage. Funny that Sam Abuelsamid (who wrote the piece in the link below) is the same writer who is for mandating a gas tax (guaranteeing a higher profit margin for the oil companies) but against mandating super-efficient cars and EVs.
http://www.autobloggreen.com/2008/12/14/can-using-premium-gas-increase-your-efficiency/
This IS propaganda.
Quotes come from "10 things you should know about propagada"
http://www.nancysnow.com/10things.htm
Gas calculations from
http://www.mpgomatic.com/mileage_calculator.html
Richard 1:59PM (12/17/2008)
Is this a joke. Mpg is a way of determining how much you are going to save in terms of money, which is what most people are really interested in. Not convinced, why are people driving less when gasoline is $4.00 than when it's $1.50? It all comes down to saving money. This theoretical cost of gasoline per mile is nonsense.
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Dave 2:59PM (12/17/2008)
Hmm, let's compare 3 recent cars my family has owned:
1. 95 Honda Civic - average 33mpg
2. 03 Subaru WRX - average 24mpg
3. 08 Toyota Prius - average 46mpg
Note: all averages are are actual numbers based on our driving
All three cars are similarly sized, in fact, the Prius is the largest and most comfortable to drive with our two kids on long trips. And it uses significantly less fuel than the Civic and WRX.
The 2010 Fusion is another car we are interested in - as our kids get larger, a bit more hip room would make us all more comfortable on long road trips - it reportedly will be rated around 40mpg - The car seats go into this car, and I get the Prius for commuting (needs some suspension upgrades, though for my preferences) and we significantly reduce our fuel consumption while improving comfort. Win-win!
Tonik 9:45PM (12/16/2008)
"MPG is the most common number cited when people want to understand how efficient a car is, especially in the US".
Excuse me, hello! You're not exactly Mr current affairs, are you? There is exactly *one* other country in the world where "mpg" is commonly used, but their gallons are Imperial and they already buy gas in liters! Continental Europe has been using L/100km for ages, and they are not switching to GPM anytime soon!
Going from MPG to GPM may help Americans understand their fuel consumption better, but it won't help you see how your car fares compared to what most civilized countries drive today. If it did, you might have noticed there is some catching up to do.
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GoodCheer 9:59AM (12/17/2008)
This is just what I was going to say.
Why on EARTH would we want to introduce a 3rd system of measurement? If we're going to have to learn the ratings of cars in a new system, shouldn't it be the one the lets us compare our cars to those of the rest of the world, rather than the bastard offspring of imperial units and metric standards?
RSR 10:11AM (12/17/2008)
I don't know if only Britain uses MPG system (assuming that's the one country you're referring to), but the same concept of km per liter (basically, distance per volume) is used in Asian countries; Japan and Korea for example (although Japan also uses CO2 kg / km concept).
Why do people make such conclusive remarks when they aren't sure?
Gordio 7:02PM (12/18/2008)
The point was fuel, the important variable, needs to be on the numerator and not the denominator. It has nothing to do with units of choice (miles/km or gallons/liters)
Nick 9:51PM (12/16/2008)
The Civic uses 2 gallons for 1000 miles??????
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azrael4h 10:01PM (12/16/2008)
2 MORE gallons per 1000 miles vs a Toyota Prius. Not bad, but the Prius is vastly more comfortable. And more practical. And the brakes won't fade out after 100 miles, and the transmission might last a bit longer than 40,000 miles. And you won't have to replace every swinging sensor every 1000 feet. And replace theCV half shafts at 30,000 miles. And...
paulwesterberg 11:08AM (12/17/2008)
Civic hybrid (42 mpg) was being compared, not the Civic (29 mpg).
By the way fueleconomy.gov already allows users to Switch Units to:
Gallons/100 Miles
Liters/100 km
Mike!!ekiM 10:35PM (12/16/2008)
These guys look like Oil Industry Propagandist's. Ask where's the funding coming from? Exxon?
Pick the car with the HIGHEST MPG that meets your needs. Then everybody wins, except Exxon and Saudi Arabia.
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Matt 10:45PM (12/16/2008)
The US is the only country in the world I know of that uses MPG, other countries use L/100kms. It makes much more sense when you think about it... but then you used an apostrophe in "Propagandist's" so I don't know how much sense you do have
Andy 3:14PM (12/22/2008)
These guys look like Oil Industry Propagandist's.
Their what?
Put the word "ass" at the end of the sentince. Makes more sense.
These guys look like an Oil Industry Propagandist's ass.
texmln 11:20PM (12/16/2008)
And the point of knowing the rate of fuel burn is...? When I'm low on fuel in the middle of West Texas I want my trip computer to tell me I have X miles left before I'm out of gas. I can't say that I would be very pleased if it just told me I was burning .083 gallons per mile. Pretty useless information for the average driver.
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noz 2:28AM (12/17/2008)
Why am I not surprised?
Max 3:41PM (12/17/2008)
Computers in cars typically indicate 'remaining distance' as well, not only 'mpg'.
bobash 4:45AM (12/17/2008)
Well, if you have your trip computer switched on "current consumption", you sill don't know squat.
That's what "remaining distance" function is for - and there's no difference whether the unit used is l/100km or mpg.
bruce 11:33PM (12/16/2008)
Oh, for heaven's sake... I've already had to explain this whole thing to about ten people who have emailed it to me.
This really seems like a solution in search of a problem. And the only problem it can solve is that some people can't do basic arithmetic. Worse yet, it obscures a lot of other, more real problems in favor of concentrating on one little subtlety. Yes, moving from 10 to 11 mpg gives more savings than going from 33 to 50... but going from 10 to 50 would be even better. Unless the 50-mpg car has fewer seats, or otherwise can't perform the same mission, which makes the whole issue less black-and-white than these people seem to think.
Using the reciprocal value, as in Europe, might well make sense, but even that won't tell you the whole story if you carpool, or if you ever have to haul a coffee table or pick up a carload of drunk friends from the bar. In other words, don't count on gallons-per-mile to reveal some previously hidden "illusion," as this individual claims.
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