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Old 02-08-2011, 09:18 PM   #37 (permalink)
darcane
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Quote:
Originally Posted by AeroModder View Post
I might be looking at things differently, but I was looking at 10% of 50 MPG is 5, and 10% of 20 MPG is 2, and 5 > 2. It might look different under another scale, but I'm not accostomed to using gal/100 mi. or l/100km.
The conventional way mileage is calculated in the US is really not intuitive. It's calculated on a per gallon basis, but you don't drive until you've used a certain amount of fuel, you drive until you get where you are going (i.e. a certain distance).

Look at it another way.
If your vehicle runs at 50mpg for 100 miles, you've used 2 gallons of gas.
If your vehicle runs at 20mpg for 100 miles, you've used 5 gallons of gas

If both improve by 10%:
The 55mpg vehicle uses 1.82 gallons to go 100 miles for a savings of .18 gallons.
The 22mpg vehicle uses 4.55 gallons to go 100 miles for a savings of .44 gallons.

Which is the bigger gain?

It's still far more useful to talk percentage than absolute mpg improvements.
If you instead improved each by 5mpg:
The 55mpg vehicle uses 1.82 gallons to go 100 miles for a savings of .18 gallons.
The 25mpg vehicle uses 4.00 gallons to go 100 miles for a savings of 1.00 gallon.

For a Prius, 1mpg is statistically insignificant. For my full size truck, it's huge.
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