calculated vs. computer MPG - Please post your results

Discussion in 'Gen 3 Prius Fuel Economy' started by F8L, Jul 10, 2009.

  1. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    24,808
    14,101
    0
    Location:
    Huntsville AL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    Welcome to PriusChat:
    When you get a chance, reset a trip meter along side a mile marker on a long segment, say 50+ miles. At the end, record the trip meter distance and mile marker. Alternatively, compare a GPS distance reading with a reset trip meter. What I've found is the distance reported by the car is off by 5-6%.

    To solve the problem, I put over-sized tires whose revs/mile gave me an accurate trip meter, odometer, and MPG.

    Bob Wilson
     
  2. FroggyTaco

    FroggyTaco Member

    Joined:
    Dec 4, 2011
    211
    57
    3
    Location:
    Paso Robles, Ca
    Vehicle:
    2013 Prius
    Model:
    Two
    What size did you end up using?
     
  3. bwilson4web

    bwilson4web BMW i3 and Model 3

    Joined:
    Nov 25, 2005
    24,808
    14,101
    0
    Location:
    Huntsville AL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Plus
    #1183 bwilson4web, Feb 28, 2016
    Last edited: Feb 29, 2016
    RMB likes this.
  4. Mr Gadget

    Mr Gadget New Member

    Joined:
    Dec 17, 2016
    20
    14
    0
    Location:
    Great Smoky Mountains TN
    Vehicle:
    2013 Prius
    Model:
    II
    I'm finding 2-4 MPG off from Computer to hand calculations (Computer being higher by 2 to 4)
     
  5. pakitt

    pakitt Senior Member

    Joined:
    Aug 10, 2009
    2,013
    1,211
    0
    Location:
    Colorado
    Vehicle:
    2021 Prius Prime
    Model:
    Limited
    My Gen 4 is about 4-5% off (MFD is optimistic wrt reality). This has improved from Gen 3 which was 6-7% off.
     
  6. FroggyTaco

    FroggyTaco Member

    Joined:
    Dec 4, 2011
    211
    57
    3
    Location:
    Paso Robles, Ca
    Vehicle:
    2013 Prius
    Model:
    Two
  7. Madjik_Man

    Madjik_Man Junior Member

    Joined:
    Nov 7, 2016
    50
    18
    0
    Location:
    Boulder, CO
    Vehicle:
    2010 Prius
    Model:
    I
    My first full tank fill up:

    Display readout: 51.2 mpg
    Actual calculated: 47.6 mpg
     
  8. TheMerk

    TheMerk Junior Member

    Joined:
    Mar 19, 2017
    6
    12
    0
    Location:
    Phoenix, AZ
    Vehicle:
    2013 Prius
    Model:
    Three
    My first tank on my new to me, 1 owner CPO 2013:

    Display: 46.7
    Calculated: 44.3

    Still light years better than my gas Jetta:)
     
  9. runnyeggs

    runnyeggs Junior Member

    Joined:
    Jul 22, 2017
    19
    1
    0
    Location:
    NV
    Vehicle:
    2013 Prius
    Model:
    III
    Funny. I sold my 2001 Jetta to get my 2013 Prius. I always get around 41 mpg. I don't know how you guys get your 45s. My car does have 16inch wheels. So the calculated is probably in the 30s. What a disappointment.
     
  10. harrysprius

    harrysprius Active Member

    Joined:
    May 23, 2017
    277
    126
    0
    Location:
    Nashville, TN
    Vehicle:
    2010 Prius
    Model:
    V
    There's a one week average on economy mode from my unscientific test.
     
    RMB likes this.
  11. James Greco

    James Greco Junior Member

    Joined:
    Jun 5, 2013
    3
    0
    0
    Vehicle:
    2012 Prius
    Model:
    II
    When I first got my 2012 in 2013, I calculated the difference between displayed and calculated for the first few months. Based on probably 5-6 months of data, I found that the displayed was typically 3-4 MPG more optimistic than the actual. That was mainly during the spring/summer months, and my MPG were in the high 50s/low 60s. My rule of thumb is to subtract 3 mpg from the displayed value. I always keep the car in economy mode. When I need additional power, I just mash the gas peddle. ;)
     
  12. Prius Maximus

    Prius Maximus Senior Member

    Joined:
    May 3, 2004
    892
    751
    1
    Location:
    Northeastern IL
    Vehicle:
    2014 Prius
    Model:
    Three
    After over 1,000 gallons of gas, 125+ fill-ups, and 55,000 miles, my lifetime display averages to 53.7 mpg while my calculated lifetime average is 52.04 mpg.

    A difference of 1.66 mpg.
     
  13. WilDavis

    WilDavis Senior Member

    Joined:
    Feb 4, 2014
    2,463
    2,118
    49
    Location:
    Top RH Corner of RH Coast on L side of The Pond
    Vehicle:
    2009 Prius
    Model:
    II
    Edit: Removed since the .pdf file was unreadable! o_O:(:mad:
    3rd attempt:
     

    Attached Files:

    #1193 WilDavis, Sep 7, 2017
    Last edited: Sep 7, 2017
  14. Mendel Leisk

    Mendel Leisk Sand Pounder

    Joined:
    Oct 17, 2010
    46,041
    32,877
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    ^ A difference of about 3.2%.


    For a similar data point:

    3393 liters (135 fill ups, typically with just under 1/2 tank remaining), and 68,817 kms, works out to 4.93 liters per 100 km (47.7 miles per US gallon).

    My average displayed fuel economy is 4.60 liters per 100 km (51.1 miles per US gallon).

    The variation there is 7.2%.

    There's maybe a bit of apples/oranges there: the first value is a single calculation, using the total fuel and total distance, whereas with the second all I can do is average all the displays. But I don't think it matters much.
     
  15. spiff72

    spiff72 Member

    Joined:
    Jan 25, 2011
    184
    37
    0
    Location:
    West Michigan
    Vehicle:
    2010 Prius
    Model:
    IV
    I may have posted this before, but my lifetime average is 45.5 mpg, and the "average" of all my percent error calculated (each tank) is 6.4% (computer always reads high).
     
    Mendel Leisk likes this.
  16. mysticeyes

    mysticeyes Junior Member

    Joined:
    Jun 25, 2017
    21
    8
    0
    Location:
    Maryland USA
    Vehicle:
    2015 Prius
    Model:
    Three
    My Prius is not used as a daily driver, so in nearly three months of ownership I've put less than 1,000 miles on it. This is about my first fillup.
    Miles: 475.9
    US gallons: 8.251
    MPG: 57.7 (calculated), 60.8 (display), 5.37% difference.
    Actually, the real mpg should probably be higher than that, because I wasn't quite sure that the tank was full when I got the first click, so I squeezed more into it until I got the second click. Now I know that the filler "neck" holds a quarter of a gallon. Using the figure of 8.0 gallons, my mpg would be 59.5. I think that is acceptable fuel economy for the first tankful in my first Prius :).
     
    Mendel Leisk likes this.
  17. Mendel Leisk

    Mendel Leisk Sand Pounder

    Joined:
    Oct 17, 2010
    46,041
    32,877
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Another tank or two, and any disparities in your fill technique will cancel out. That's very good mileage, you must be consolidating trips.
     
  18. mysticeyes

    mysticeyes Junior Member

    Joined:
    Jun 25, 2017
    21
    8
    0
    Location:
    Maryland USA
    Vehicle:
    2015 Prius
    Model:
    Three
    "Another tank or two, and any disparities in your fill technique will cancel out. That's very good mileage, you must be consolidating trips."

    Yes, since I have the convenience of another car for daily abuse, I can choose to drive the Prius on trips of at least 10 miles, or on strings of short runs. I try to drive it at least once every 10 days or so, and I always find reasons to visit family and friends in other towns. This is my first Prius, but I did put close to 300 thousand miles on an Insight. I discovered that over the years I had worked out for myself various driving techniques for fuel efficiency, usually by trial and error and by watching the real time MPG display, though I try to never hold up traffic. I'm sure I still have a lot to learn. Since the weather affects fuel use - quite a bit - I'm curious about what will happen this fall.
     
  19. jerrymildred

    jerrymildred Senior Member

    Joined:
    Oct 28, 2016
    10,261
    12,586
    0
    Location:
    Tampa, FL
    Vehicle:
    2017 Prius Prime
    Model:
    Prime Premium
    Since my first fill up in the PiP on January 15 this year, my calculated raw mpg averages 89.71 mpg vs. the HSI display guesstimate of 94.71. So it's about 5.6% optimistic. That covers 11,984 miles.
     
  20. Mendel Leisk

    Mendel Leisk Sand Pounder

    Joined:
    Oct 17, 2010
    46,041
    32,877
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Consider getting a smart charger, and maybe install a quick connect for it. Our usage is not that sporadic, but I keep it on such a charger, whenever there's a day or three idle time.
     
Loading...