Sunday, June 12, 2011

MPG vs GPM

All over in the US, we use mpg, Miles Per Gallon. This is the way we compare vehicles in how efficient they are. Unfortunately, its a misleading measurement. It really should be Gallons Per Mile, or better yet, Gallons Per Hundred Miles. We could even go to the bastardization of metric and imperial, and go with Gallon per Kilo-Mile... For my examples, I'll use gp100m..In this example, there's two vehicles.. The first vehicle, a truck, is rated at 10mpg.. The second vehicle, a full size car, is rated at 20mpg.. Say each owner of the vehicle decides to upgrade to something more efficient, but still within the same class... The truck owner finds one at 12.5mpg, and the car owner finds one that is 25mpg.. Which owner saves more fuel?

The truck owner.

Even with twice the number in increase in mpgs, the truck owner made the better deal.Here's how you see that. Each owner drives his vehicle 100 miles, and we calculate how fuel is burned. In the original truck at 10mpg, going 100 miles means they burned 10 gallons. With their new truck, they burned only 8, a savings of 2 gallons!

The car on the other hand, with a original rating of 20 mpg, burned 5 gallons going the 100 miles. In his new car, with 25mpg, he burned 4.. He saved a single gallon...

How lets switch to the gp100m measurement, and see how easy it is to compare.. The original trunk got 10 gp100m.. The new truck gets 8 gp100m.. The original car gets 5 gp100m, and the new car gets 4 gp100m. Much easier to see the difference. The smaller the number, the more efficient.
This also makes it easier to calculate how much money it'll cost you to go a particular distance. You know you're going 300 miles, so take the gp100m * 3, thats the number of gallons you use. Then multiple by the cost of the cost. There you go.

Unfortunately, the mpg way of measuring things is ingrained in our American heads, and unlikely to change any time soon. Just like the anti-diesel bias in the US.. Why can't I get the European diesel version of my car? I mean, my car gets a 'great' 28mpg, highway.. But the equivalent diesel in the UK: 51mpg.. And it accelerates faster! Close-minded US officials. They had a 70's Detroit diesel car, and now think that all diesels are bad. *sigh*.

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