EcoModder Forum Weighted Combined MPG Rating Calculation?

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 05-29-2008, 12:22 PM #1 (permalink) EcoModder     Join Date: May 2008 Location: Southern Oregon Posts: 111 GeRide - '89 Geo Metro *XFi 90 day: 54.26 mpg (US) Thanks: 0 Thanked 0 Times in 0 Posts 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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 05-29-2008, 12:33 PM #2 (permalink) Master EcoModder   Join Date: Apr 2008 Location: Earth Posts: 303 Pushrod - '02 Chevrolet Cavalier Thanks: 0 Thanked 8 Times in 4 Posts 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.
 05-29-2008, 12:43 PM #3 (permalink) Administrator     Join Date: Dec 2007 Location: Germantown, WI Posts: 11,184 CM400E - '81 Honda CM400E 90 day: 51.49 mpg (US) Daox's Grey Prius - '04 Toyota Prius Team Toyota 90 day: 49.53 mpg (US) Daox's Insight - '00 Honda Insight 90 day: 64.33 mpg (US) Swarthy - '14 Mitsubishi Mirage DE Mitsubishi 90 day: 56.69 mpg (US) Thanks: 2,485 Thanked 2,553 Times in 1,537 Posts 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. __________________ Current project: A better alternator delete
 05-29-2008, 01:07 PM #4 (permalink) Hypermiler     Join Date: Dec 2007 Location: Texas Posts: 2,321 PaleCivic (retired) - '96 Honda Civic DX Sedan 90 day: 69.2 mpg (US) PaleFit - '09 Honda Fit Sport Team HondaWagons 90 day: 44.06 mpg (US) Thanks: 611 Thanked 432 Times in 282 Posts 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. __________________ 11-mile commute: 100 mpg - - - Tank: 90.2 mpg / 1191 miles
 05-29-2008, 01:11 PM #5 (permalink) EcoModding Lurker   Join Date: Apr 2008 Location: Colchester, CT Posts: 38 POS - '97 Ford Aspire 90 day: 47 mpg (US) Thanks: 0 Thanked 1 Time in 1 Post www.fueleconomy.gov has a feature to put your acutally ratio, annual miles, and price per gallon. __________________