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Old 05-29-2008, 11:22 AM   #1 (permalink)
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Weighted Combined MPG Rating Calculation?

Just curious...

Is there a calculation (or better yet... an actual online calculator) that figures out a combined MPG based on the % of city and highway driving you do?

So by this I mean that my Geo is rated for 43city and 51highway. The combined listed is 46mpg. But wouldn't this combined mpg be for 50% city and 50% highway?

Let's say I drive 40% city and 60% highway. Using these numbers is there a way to calculate a weighted combined mpg based on the EPA numbers?

Sorry... I don't do math so good. LOL

Thanks! Just curious really.

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Old 05-29-2008, 11:33 AM   #2 (permalink)
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There are different ways of chopping up the numbers.

Does 50% highway mean...

50% of your miles are traveled on the highway?
You spend 50% of the time on the highway?
You burn 50% of your fuel on the highway?

I'd think the first is the most likely. The EPA's numbers are based on 45% highway, 55% city driving.
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Old 05-29-2008, 11:43 AM   #3 (permalink)
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The EPA numbers really shouldn't be taken that literally. They are a standardized test and really more of a generally guideline. I like to think of them as a descent guess. There are too many variables that affect mileage. There is no test in that can predict what you'll get.
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Old 05-29-2008, 12:07 PM   #4 (permalink)
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The epa combined is weighted 45/55%. I don't remember which one is weighted more, but rounding it pretty much cancels that out anyway.

To calculate it, figure the gallons used in each and then divide by the total miles. Example from my car (33 city 38 highway)
25% city = 25 miles @ 33mpg = 25/33 = .76 gallons
75% highway = 75 miles @ 38 mpg = 75/38 = 1.97 gallons
Total = 100 miles / 2.73 gallons = 36.6 mpg.
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Old 05-29-2008, 12:11 PM   #5 (permalink)
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www.fueleconomy.gov has a feature to put your acutally ratio, annual miles, and price per gallon.

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