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Old 06-19-2008, 03:32 PM   #1 (permalink)
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Why "Gallons Per Mile" (or L/100 km) makes more sense

“Miles per gallon is misleading and can play tricks on our intuitions”

Duke University professors show experimentally what many of us have been saying for a while: talking about fuel consumption in terms of "MPG" is problematic.

Quote:
(Duke) professors Richard Larrick and Jack Soll ran a series of experiments showing that the current standard, miles per gallon or mpg, leads consumers to believe that fuel consumption is reduced at an even rate as efficiency improves. People presented with a series of car choices in which fuel efficiency was defined in miles per gallon were not able to easily identify the choice that would result in the greatest gains in fuel efficiency.For example, most people ranked an improvement from 34 to 50 mpg as saving more gas over 10,000 miles than an improvement from 18 to 28 mpg, even though the latter saves twice as much gas. (Going from 34 to 50 mpg saves 94 gallons; but from 18 to 28 mpg saves 198 gallons).
The authors then tested people by presenting fuel consumption ratings in the form of gal/100 miles, and the mistaken impressions were corrected.

Not surprisingly, the authors call for for a change in the way consumer publications and manufacturers report fuel consumption.

Full article:
http://www.dukenews.duke.edu/2008/06/GPMFuqua.html

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Old 06-19-2008, 06:07 PM   #2 (permalink)
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I completely agree with the g/100 mi. It instantly removes that complicated translation of how much money is saved (or spent, in total) on a tank (if you're money-motivated).

So, what I've noticed about L/100 km is that the single-digit + one decimal place is finicky in instant FE displays. How about dL/100 km and move the decimal over one? I suppose it's easy enough to do mentally. Plus, the perception means little, having been exposed to the old "English" system forever.

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Old 06-19-2008, 06:12 PM   #3 (permalink)
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They're asking the wrong question. Why nitpick about whether 18-28 is better than 34-50? Just go from 18 to 50 :-)

Also, why liters/100 km or gallons per 100 miles? Why not per km or mile? Or better yet, how about a cents per mile figure at current gas prices? I like that one: with the Insight averaging better than 70 mpg, I go 4 times as far on a gallon as someone with a 17.5 mpg SUV, so I'm effectively using $1/gallon gas :-)
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Old 06-19-2008, 06:39 PM   #4 (permalink)
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Quote:
The authors then tested people by presenting fuel consumption ratings in the form of gal/100 miles, and the mistaken impressions were corrected.

Not surprisingly, the authors call for for a change in the way consumer publications and manufacturers report fuel consumption.
18 mpg = .0555 gpm
28 mpg= .0357 gpm
34 mpg= .0294 gpm
50 mpg= .0200 gpm

Overheard at the car dealership:
"But Errrrnieee, this Canyonero uses only .0355 more gas than that tiny little car YOU want to get. You are such a cheapskate for worrying about an itsy-bitsy .0355 of gas. Lucy's husband Ricky got HER a Canyonero, and if you don't get me the Canyonero too, no nookie for you.

Heh. nookie nookie nookie. The word filter is powerless
bbbzzzzZZZZAP!
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Old 06-19-2008, 07:15 PM   #5 (permalink)
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I hate L/100km personally. But it makes fuel used over long distances easier to calculate. When you change a system of measurement people lose a historical sense of what was. How many L/100km does a 55 chevy get?
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Old 06-19-2008, 07:29 PM   #6 (permalink)
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MPG is fine. If people can't figure it out, I see it as an idiot tax.
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Old 06-19-2008, 07:42 PM   #7 (permalink)
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In addition, there is another twist in calculating FE. For example, my present average is about 41-42 mpg. I can easily get 46 mpg if I take another route to and from work. However, that particular route is long enough to cost me an extra 12 more cents a day in gas than the route with lower mpg, which is shorter. Therefore the FE of the engine and the FE of the route are in conflict.

My ego makes me want to take the higher mpg route so that I can brag about my efficiency. Logic and my conscience demand I take the more efficient route, which has lower mpg.
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Old 06-19-2008, 08:55 PM   #8 (permalink)
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Maybe that should be an additional function on your trip meters. You plug in the cost of gas, it displays the cost of your trip...
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Old 06-19-2008, 09:13 PM   #9 (permalink)
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I like Miles per Dollar best.
Hard to rate vehicles that way, but . . . .
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Old 06-19-2008, 10:05 PM   #10 (permalink)
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i like L/1ookm, it looks like its already in scientific notation!

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