MPG Is Stupid
Edmunds.com
Member, Administrator, Moderator Posts: 10,316
MPG Is Stupid
Edmunds' well-reasoned look at why miles per gallon is far from the best means to measure fuel consumption.
Tagged:
0
Comments
"simple" procedure....
Going to Las Vegas yesterday, a friends new 528 display read out
the mpg as we drove(36.7), not sure I'd like to see .0272479
gallons per mile, if you know what I mean.
I don't think this argument is sufficient to warrant a change, nor does it protect consumers from companies inflating their fuel efficiency ratings.
As another poster mentioned, the best thing we could do is make the EPA tests better reflect real-world driving conditions and consumption.
The crux of the article focuses on the idea that -
miles / gallons is somehow less accurate and leads to more misconceptions than gallons / mile.
Its the same number. Just divided differently.
Particularly annoying is the section "It's All in Your Head." -
You're attempting to make the point that it is difficult to calculate the amount of gallons used for a 200 mile trip because it involves doing division. Whereas, multiplication is so much easier, if only!
Its the same basic mathematical function. It really is.
Gallons used = 200/18 (if expressed in miles per gallon)
or
Gallons used = 5.6/100 * 200 (if expressed in gallons per mile)
I fail to see your point that the latter is somehow "more straightforward" than the former. If anything, its more complex if your trip length is anything other than a multiple of 100.
The key point is that the "best" unit is useless discussion unless you know the primary question. What the EPA is saying by keeping MPG on window stickets is that the most common question on car buyers minds is, "How far can I go on 1 gallon of gas with this particular vehicle?" Isn't it easier to just answer that question in 1 glance?
If you want to make a point about window stickers being inaccurate/uninformative, write an article describing the city/highway testing cycles and how they are/are not similar to modern day car usage and/or the leeway car companies have in the production of those numbers.
Efficiency is measured as a ratio between input and output. For cars it's BSFC (brake specific fuel consumption) or Torque per unit-fuel @ rpm used. That it measure the efficiency of converting between input energy and output energy. Look up any automotive engineering book and this--BSFC--is the definition of efficiency you'll see, which is not a single figure but varies over rpm, not MPG or GPM.
You don't measure an AC/DC power supply's efficiency just by how much electricity it consumes. That's frugality or economy. You measure by how much it consumes (which can be over time or instantaneous) vs how much DC power produces.
You don't measure a refrigerator's efficiency just by how much electricity it consumes. That's frugality or economy. You measure by how much it consumes (which can be over time or instantaneous) vs how much cooling power it produces.
I think you're missing the point of this article. You are correct in that there's nothing technical wrong with the current miles/gallon value advertised in the US. Whether you use mpg or gal/mile, you are correct that it's all the same data, just presented in a different format. The point of this article is that mpg is MISLEADING to consumers, completely unintentionally but misleading nonetheless.
By using mpg, you might think that 14 mpg vs. 15 mpg isn't that big of an economy gain, but it's actually a helluva big gain compared to 49 vs. 50 mpg.
I just happened to run this analysis a couple years ago when I was buying a new vehicle and comparing vehicle cost vs. total monthly cost inclusive of fuel economy. :
Assumptions: 12000 mi/yr
mpg $3/gal
10 $300
15 $200
20 $150
25 $120
30 $100
35 $86
40 $75
45 $67
50 $60
You'd save $100/month in gas cost if you ditched that 10mpg bubba truck for a 15mpg SUV. Huge change there. However, if you ditch that 45mpg Hyundai hybrid for a 50mpg Prius, you'd only save $7/month and hence might be considered an idiot if you did so purely to save on gas costs.
Same incremental mpg gain between the two vehcile scenarios but radically different fuel cost changes.
The net change in gas cost for a certain mpg change completely depends on the reference mpg. It's a crappy indicator because the amount of gas used does not response linearly to mpg change.
On the other hand, gallons/mile allows for a linear response between gas used and gpm. If your gpm decreases by 10%, you're going to spend 10% less on gas, and visa-versa. It's simple.
That's the point of this article.
That said, your example of planning a road trip is why, given peoples poor math skills, mpg is better. Very few plan on how much gas it takes to take a road trip. For those that do, the math is easy (not to mention very few trips are rounded to the 100 miles) What people do need to figure out while driving is how much farther I can go with my remaining gas. Say I have a 16 gallon tank in my 18 mpg car. I am at the 1/4 mark. Sans reserve I know I have about 4 gal of fuel. At 18mpg, I can go approximately 72 miles. Now, tell the average person how much farther they can go with a 1/4 tank of fuel (4 gals) in a car that gets 5.5 gp100 and I think you will have some very confused people - remember, these people think, as you have displayed, that gpm is different than mpg, and not just a simple reciprocal.
It is more logical.
It's not per miles, it is per 100 miles; So it would read 2.7ghm
That said, it is a clearer comparative indication of fuel usage in some ways. But a less clear indicator of fuel consumption in other ways. Both methods have pros and cons for those that do not like to do math
As for metric - all our maps, road signs, speed, etc are in miles. All our pumps are in gallons. The cost to change to liters and km would be huge for absolutely no gain whatsoever.
People that find math hard, with find it hard no matter what. Giving them a reciprocal wont help. My apologies, but they are just stupid and seem to be operating at the math level of a 2nd grader, proven by your point that people find addition and multiplication easier - since subtraction and division are technically addition and multiplication, respectively.
It just sounds sorta familiar ....
http://www.greencarreports.com/news/1019426_miles-per-gallon-is-just-stupid-no-really-it-is
best, jv.
A car that's coasting while using the GPM figure will get 0 gallons per 100 miles.
To the person who wrote "I just think its a stupid argument/waste of an article to say, "no, the inverse of this number is clearly the better number." I point to the above. Why so upset about it? Is it really fair to call something "stupid" when you don't understand it?
look what you made me do.
http://xkcd.com/386/
Why isn't anyone focusing on how poorly the average North American navigates our roadways i.e., jackrabbit starts, speeding, staying on the gas until your a foot away from a stop light/sign etc, etc. How come you didn't discuss poorly maintained vehicles/tires as well. Seems to me there's a lot that can be done everyday by almost everyone to improve fuel efficiency!! What about LRR tires? I'm willing to bet the list is actually quite a bit longer than that which I've suggested. Get the "word" out, if you will, and forget the article on gpm please!!!!!!!!!
Here in Europe, the standard is : L/100km, since i've remember.
Sometimes the change is good!
In this case, the best choice is gp100
Maybe if the measurement was gallons per 1000 miles, no decimal, it would be simple and accurate enough.
I wonder how EPA came with that idea of measuring, anyway. Was it because US always jas to be different than rest of the world?
2018 430i Gran Coupe
X/Y = Miles per gallon (MPG)
Y/X = Gallons per mile (GPM)
(Y/X)*100 = Gallons per 100 miles (GP100)
To say any one measure is better or worse, or more or less intuitive, is ridiculous. There is absolutely no point to this article. It's like saying you can buy 3 apples for $1 each (measuring in terms of cost per apple), or you can pay $10 for 10 apples (measuring in terms of what 10 apples cost). Same information. No more relevant or useful either way.