windows up or down

Discussion in 'Toyota' started by wjacobusse, Mar 17, 2009.

  1. wjacobusse

    wjacobusse Member

    2008 Toyota Yaris S Sedan - Highway MPG Testing:

    43.2 MPG - windows down, cruise control off, A/C off
    43.8 MPG - windows down, cruise control on, A/C off
    46.2 MPG - windows up, cruise control on, A/C on 50%
    49.7 MPG - windows up, cruise control off, A/C off
    (Specifics: 40 mile interstate loops, cruise control set at 66 MPH, 60-70 MPH range with cruise off.)

    Looking at these numbers makes me wonder: Is there some break-even speed where its the same whether u drive with windows down-A/C off or windows up - A/C on?
    And what about windows partially open?
     
  2. Taliesin

    Taliesin Well-Known Member

    From what I have seen, there is a break point and it depends on a few factors:

    What vehicle (mostly the CD factor and how much the windows change it, but also how well it can take the extra engine load)
    How far down are the windows
    How much AC

    For slow driving it's usually best to open the windows. Air resistance isn't as much of a factor then.
     
  3. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    I'd guess the tipping point would be somewhere in the 45-55 mph range for a sedan. I haven't found any difference with the windows cracked an inch or two.

    Of course, windows up and ac off is the best combination.
     
  4. voodoo22

    voodoo22 Cheaper than the bus

    On a side note, your numbers are great for showing people how to take their Yaris into the 50mpg zone.
     
  5. wjacobusse

    wjacobusse Member

    strange, both best and worst are with cruise control off. That doesnt make it any clearer now, does it?
     
  6. PaleMelanesian

    PaleMelanesian Beat the System Staff Member

    It just shows how the driver makes all the difference, both positive and negative.
     
  7. ksstathead

    ksstathead Moderator

    And implies that windows down hurts mpg.
     
  8. Elixer

    Elixer Well-Known Member

    Windows down an inch or two is probably the best as it doesn't make nearly the same impact on aerodynamics. I also think air conditioning would work well when used in combination with DWL - Use it on downhills and flats, but turn it off when going uphill. Alternatively use it during P&G only during the pulse. I would imagine the break even point around what others have said ~ 45-55mph for most vehicles. On my car having the windows down doesn't seem to affect my glides below 45mph. However I can definitely tell it takes more gas when the windows are down at 60 mph+
     

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