Fuel consumption: MPG or GPM? - Roger Jones
Interesting perspective on fuel consumption here:


Edited by Roger Jones on 11/03/2009 at 14:16

Fuel consumption: MPG or GPM? - kayks
In our country, we buy fuel is litres and measure distances in miles. The two figures quoted for fuel efficiency are Litres/100 kilometres (the EU standard) and Miles per Gallon. I think both these numbers are pretty useless. Why not use Miles per Litre and Litres per 100 Miles?
Fuel consumption: MPG or GPM? - Lud
Continentals are used to l/100km, but we are used to mpg. The conversion is easy with a calculator. You work out the miles per litre and multiply the answer by 4.546 to get mpg. You know that if you are getting 10 miles to the litre your car is bettering 45mpg.

I imagine one day we will have to have kilometres here as they already do in Australia and New Zealand. I am against it on grounds of cost (and downright prejudice).

Of course the original link is American, relevant more there than here. We don't have all that many sub-17mpg cars.

Edited by Lud on 11/03/2009 at 14:36

Fuel consumption: MPG or GPM? - kayks
Its an easy conversion, Lud, but I don't want to have to do it all the time despite being comfortable with mental arithmetic! Call me lazy. Wonder what the mathematically-challenged set of people think?
Yes, the article is American, sub-17mpg "cars" are common out there, but the science is still the same ...
Fuel consumption: MPG or GPM? - Andrew-T
If you are getting 10 miles to the litre your car is bettering 45mpg.

I have been shouted down on this forum before, for calling for MPL instead of MPG, as no-one has bought in gallons for years. Why should we multiply by 4.546 (an awkward number) just to preserve a sacred tradition?

Actually it is easier (and just as accurate) to use 11 MPL = 50 MPG. Personally I aim for 13 MPL which is about 59 MPG ... :-)
Of course the original link is American ..

and the American gallon isn't the same as ours anyway (but at least the miles are, I think).

Edited by Andrew-T on 11/03/2009 at 17:59

Fuel consumption: MPG or GPM? - Lud
It's really a question of meaning Andrew-T. 10 or 11 mpl may be easy to understand, but when your smalliish car returns 7.9 mpl or 8.3, you want to know whether you are running at a worrying sub-36mpg or a more reassuring 38 (nearly)...
Fuel consumption: MPG or GPM? - J Bonington Jagworth
I'm tempted to say that only an American would think that 3 mpg was the same difference at 14 mpg as it is at 33!

In any case, any calculation of mpg (which I do occasionally) is simply confirmation of what you already know, if you keep an eye on your consumption. If you don't, then presumably you don't care or want to know.

It may be just familiarity, but mpg seems a more useful real-world measurement, like pints of beer and pounds of bananas. I'm also intrigued by the odd coincidence that 1 (UK) gallon is 4.54 litres and 1 pound is 454 grams. What are the odds against that..?
Fuel consumption: MPG or GPM? - Andrew-T
What are the odds against that..?

Very short odds. A gallon = 8 pints, each containing 20 fluid ounces = 160 fluid oz. = 10 pounds = 4540 grams.

1 litre = 1000 grams.

Very small differences due to the variation in density of water with temperature, etc.

Edited by Andrew-T on 11/03/2009 at 18:13

Fuel consumption: MPG or GPM? - J Bonington Jagworth
"Very short odds"

You're so right. I'd quite forgotten about the relationship between gallons and pounds. Wood, trees and all that.. :-(
Fuel consumption: MPG or GPM? - GJD
Funnily enough I've changed my mind a bit since this one last came up. I previously thought that since it's a simple calculation, I don't really care about the units. That's still partly true - whether the unit of volume is gallons or litres doesn't bother me at all. But using distance per unit volume does feel the wrong way round with volume as the denominator.

Everything I think about the way I drive is in particular, known distances - whether it's a trip down the shops, the commute to work, a particular journey I'm planning, annual usage, service interval etc. So when I think about fuel consumption, either for today's journey, or a years' budgeting or whatever, the distance involved is always fixed and the volume of fuel is the variable. What I want to know is: over that distance, how much fuel could I save between car A and car B? Volume per unit distance answers that question more directly. Knowing that car B does another 5 miles on the same gallon isn't immediately helpful because I don't want to do another 5 miles. Knowing how many fewer gallons per 100 miles car B uses however is exactly what I need because I know exactly how many hundreds of miles I am thinking about.

Moreover, mpg is made harder because how much fuel car B saves me over a fixed distance depends on whether that 5mpg benefit is the difference between 20 and 25 or 40 and 45. On the other hand, an improvement of 1 gallon per hundred miles is the same fuel saving over my fixed distance regardless of the absolute gallon per 100 mile figures.

I am quite capable of doing the calculations, but since I happen to have been doing them a lot lately I have come to the conclusion that the only thing mpg has going for it in this debate is its familiarity.
Fuel consumption: MPG or GPM? - redviper
Ive just had a play with the GM Vehicle Fuel Economy and CO2 Calculator site, that was posted previosly.

And I love the way it tells you how many Barrels of fuel, for Example a Hummer will use 23 "barrells of fuel a year", AFAICS is does not state how much is in the barrel.

Also it allows you tailor the results, by giving you check boxes for

. My trunk or cargo bay has 100 pounds of stuff in it

and the one i find most amusing

. My Check Engine light is on