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Instantaneous MPG vs Average

Discussion in 'Prius c Fuel Economy' started by Hodr, Jul 13, 2013.

  1. Hodr

    Hodr Junior Member

    Joined:
    Jun 12, 2013
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    Vehicle:
    2012 Prius c
    Model:
    Two
    I have been trying to teach myself the absolute best way to drive my to and from work routes, mostly for fun as the extra 2-3 MPG doesn't really matter. After receiving my OBD II reader and monitoring the instantaneous MPG I found that I never go above 60 mpg or so unless I am on a slight decline or using battery power.

    If the vehicle has a maximum flat road MPG of 60, then over the course of a round trip (ending in the same location you started) you should never be able to get above this value unless you end with less battery than you start with or the vehicle somehow gains more going downhill than is lost going uphill (I.E. you lose 15% going up the grade, but can shut off the engine going down so you actually recoup 20%).

    I think this has helped me to understand why I never seem to get more than ~60 as a max round trip value (and usually closer to 50) without draining the battery, but I often see people post on here with 70s and 80s and I wonder how they do it.

    I think maybe the 99mpg (which is actually recorded as 255 by the OBD II) when on battery skews the average far more than it should for heavy battery users, which might also explain the difference between their results and their real world measured values (usually -2mpg or so).

    I am generally happy whenever I can get more than 50mpg as most of my trips are only a couple of miles. I have been playing the MPG for a while, and just want to find a way to more consistently hit the upper 50s to low 60s.
     
    #1 Hodr, Jul 13, 2013
  2. ztanos

    ztanos All-around Geek!

    Joined:
    Jan 10, 2013
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    Location:
    Cumming, Georgia
    Vehicle:
    2012 Prius c
    Model:
    Four
    Try driving in the Eco range when driving faster than 45. On the flats and even slight inclines, you can get around 70 mpgs or higher.
     
    #2 ztanos, Jul 13, 2013
  3. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

    Joined:
    Feb 14, 2010
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    Location:
    Rocky Mountains
    Vehicle:
    2006 Prius
    Model:
    Three
    Driving on a flat surface at a constant speed with no starts or stops, and you can't get above 60mpg, then you are correct.

    But now factor in "city" driving. Lets continue the flat road and you are getting 60mpg. There is a stop light 1/3mile ahead of you that's red. Let off the gas and glide, no engine power and the only electricity coming from the battery is power subsystems and not being used as motive power. So now with 60mpg you get 1/3mile with infinite mpg. The better you get at timing you won't have to fully stop so getting back up to speed takes less energy.

    This is sort of the foundation of "pulse and glide". Pulse with medium-high power to get up to a speed + 5mph, then glide to speed -5. Pulse back up to speed+5, glide back down. This works on flat roads. Then for hilly terrain you can do the same sort of thing, but you glide up a hill or apply light power to get up the hill while losing speed. Then you can glide down the hill and recoup most speed or if it is small enough of a hill apply some power down the hill.
     
    #3 2k1Toaster, Jul 13, 2013
    SquallLHeart and minkus like this.
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