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MPG for trip w/o having to reset MFD!

Discussion in 'Gen 2 Prius Fuel Economy' started by Whiteyprius, Mar 15, 2008.

  1. Whiteyprius

    Whiteyprius Active Member

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    Some of you number-hounds and mpg fiends may appreciate this -- If your MFD was reset at your last fillup, the following formula will yield your mpg on any length trip w/o your having to reset the MFD. Before beginning your trip, record the miles on the tank and your current mpg. Then at the end of your trip record the same thing, complete the below calculation, and bingo, you have your mpg’s for that particular trip.

    Solve for x (mpg for trip)

    a = beginning miles
    b = beginning mpg
    c = ending miles
    d = ending mpg

    x = c – a
    (c / d) – (a / b)

    EXAMPLE:

    Today, I took a trip to the mountains. Before I left my MFD said that I had been 226 miles on the tank and had averaged 47.8 mpg. When I returned, my MFD said that I had 362 miles on the tank, and was now averaging 49.5 mpg. Enter the data:

    x = 362 – 226
    (362 / 49.5) – (226 / 47.8) (362 divided by 49.5 minus 226 divided by 47.8)

    x = 136 (miles driven on trip)
    7.31 – 4.73 (end of trip gallons used on tank minus beginning of trip gallons used on tank)

    x = 136
    2.58 (gallons used on trip)

    x = 52.71 (This figure makes sense. Several weeks ago I took almost the identical trip and averaged a bit more than 53mpg – It was raining cats & dogs today)

    I like number challenges. I hope there are some of you that will enjoy using the above. Blessings upon you all!:D (If there's something here that I've screwed up, please feel free to let me know.)
     
    #1 Whiteyprius, Mar 15, 2008
  2. joeszabo

    joeszabo Junior Member

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    Hi WhiteyPrius,

    Nice calculations, math is really magic:hail:! I wonder if more of our fellow members would benefit from / appreciate this if it were loaded into a spreadsheet?
     
    #2 joeszabo, Mar 15, 2008
  3. Whiteyprius

    Whiteyprius Active Member

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    I'm not that great with spreadsheets, but I'll give it a try - or anyone else for that matter - I've got no copyright here!:D
     
    #3 Whiteyprius, Mar 16, 2008
  4. Whiteyprius

    Whiteyprius Active Member

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    I think I've just discovered that I can't attach an Excel file here - but if you would like to create your own spreadsheet it would look like this. I can't make the spacing realistic here, but Column A would be your titles, "Beginning mileage" etc. Column B would be your values for each. Line 5, Column B's formula would be: =(B3-B1)/(B3/B4-B1/B2).

    Beginning mileage 226
    Beginning mpg 47.8
    Ending mileage 362
    Ending mpg 49.5
    Trip mpg (x) 52.6

    Again, if there is a math whiz out there that sees that I have done something screwball, let me know. Thanks!:D
     
    #4 Whiteyprius, Mar 16, 2008
  5. Bob64

    Bob64 Sapphire of the Blue Sky

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    Unfortunately, I don't think that your formula will work once people's mileage goes above 10,000 between resets.
     
    #5 Bob64, Mar 18, 2008
  6. Danny Hamilton

    Danny Hamilton Active Member

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    I think the assumption given by the original poster was that the MFD MPG was reset at fill-up.

    The idea being that you can track your tank MPG with the MFD and the trip MPG with the formula.
     
    #6 Danny Hamilton, Mar 19, 2008
  7. Spectra

    Spectra Amphi-Prius

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    Looks good Whitey, but I'm not certain where these numbers came from:

    "7.31 – 4.73 (end of trip gallons used on tank minus beginning of trip gallons used on tank)"

    Do you have a method of determining the number of gallons in your tank (to 2 decimal places) at any point in time?

    Maybe the answer's just staring me in the face, but, please explain.
    Thanks!
     
    #7 Spectra, Mar 19, 2008
  8. Whiteyprius

    Whiteyprius Active Member

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    You're right - I said "If your MFD was reset at your last fillup..."
     
    #8 Whiteyprius, Mar 19, 2008
  9. Whiteyprius

    Whiteyprius Active Member

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    No, I don't know the number of gallons in my tank. 7.31 = the MFD trip meter upon my return divided by my MPG at that point in time. Likewise 4.73 = my MFD trip meter at the beginning of my trip, divided by my MPG at that point in time. Subtract the lesser from the greater and you have the number of gallons you used on your trip. Divide the trip miles by the number of gallons used on your trip, and you have your MPG for your trip. Set your calculator, or spreadsheet field to give you the desired number of decimal places. I just find anything beyond tenths to not really be that significant.:D
     
    #9 Whiteyprius, Mar 19, 2008
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