1. Attachments are working again! Check out this thread for more details and to report any other bugs.

fuel economy: side windows, moon roof,sun roof

Discussion in 'Gen 3 Prius Fuel Economy' started by dbldbl, Mar 18, 2012.

  1. dbldbl

    dbldbl Junior Member

    Joined:
    May 5, 2010
    34
    4
    0
    Location:
    Midwest
    Vehicle:
    2010 Prius
    Model:
    IV
    Ok. At low speeds, open side windows don't affect aerodynamics and fuel economy so much. But does does affect it ? % at highway speeds. .. or so the discussion usually goes

    But with the design of the Pruis moon/sun roof - how much does the deflector help for the moon roof versus the common version that becomes just like a regular window?

    versus the sun roof (or maybe I've got this mixed up which is supposed to be which.)

    Most articles I've seen are rather vague about this.
     
    #1 dbldbl, Mar 18, 2012
  2. F8L

    F8L Protecting Habitat & AG Lands

    Joined:
    Aug 14, 2006
    19,011
    4,080
    50
    Location:
    Grass Valley, CA.
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Buy a Scangauge II and test it out. :)

    I expect a full write up on the subject by next week. You better get crackin'.
     
    #2 F8L, Mar 18, 2012
  3. ghosteh

    ghosteh Member

    Joined:
    Dec 22, 2010
    146
    57
    0
    Location:
    Illinois
    Vehicle:
    2012 Prius
    Model:
    Three
    I was on the highway yesterday (straight & level) with the cruise on, and tried experimenting with sunroof open/closed. Although fuel mileage fluxuates constantly anyway, I did see a noticeable drop (probably 4-5mpg) when I opened the sunroof at 65mph. In the city, there would be no difference.

    The deflector is there to both minimize drag and reduce turbulance inside the car. Think of an open window or sunroof as a parachute that catches wind that would otherwise be flowing across the smooth surface. The deflector bumps the airflow up a little, over the opening which would otherwise catch quite a bit more air. A deflector is certainly going to reduce your drag, but not nearly as much as an open sunroof without one.

    Incidently, I didn't see any difference with the AC on or off. I suspect that there HAS to be an impact on your mileage when using AC in a Prius, but if there is, it's so small that you can't tell.
     
    #3 ghosteh, Mar 19, 2012
  4. F8L

    F8L Protecting Habitat & AG Lands

    Joined:
    Aug 14, 2006
    19,011
    4,080
    50
    Location:
    Grass Valley, CA.
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Try it again when the interior of your car is 130 degrees and you have the AC set at 70 degrees. :) This condition is very common and that is when I saw the large losses. If it is 75 degrees inside the car and you set the AC to 70 degrees the loss is barely registered.

    http://priuschat.com/forums/gen-ii-prius-fuel-economy/97814-how-reduce-mpg-loss-because-c-use.html
     
    #4 F8L, Mar 19, 2012
  5. ghosteh

    ghosteh Member

    Joined:
    Dec 22, 2010
    146
    57
    0
    Location:
    Illinois
    Vehicle:
    2012 Prius
    Model:
    Three
    #5 ghosteh, Mar 19, 2012
  6. F8L

    F8L Protecting Habitat & AG Lands

    Joined:
    Aug 14, 2006
    19,011
    4,080
    50
    Location:
    Grass Valley, CA.
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    That's what I'm hoping for! :rockon:
     
    #6 F8L, Mar 19, 2012
    1 person likes this.
  7. qbee42

    qbee42 My other car is a boat

    Joined:
    Mar 2, 2006
    18,058
    3,073
    7
    Location:
    Northern Michigan
    Vehicle:
    2006 Prius
    Open windows affect aerodynamics at all speeds. Perhaps what you intended to say is that aerodynamics are not very important at low speeds. That is correct. Aerodynamic drag goes up by the square of the speed, and the power required to move a car against aerodynamic drag goes up by the cube of the speed.

    At high speeds open windows are a significant drag.

    The sun/moon roof top on a Prius has more drag even when shut. This occurs for two reasons: 1) The opening roof has seams and protrusions that disturb the airflow; and 2) The opening roof is flat, where the non-opening roof features a drag reducing pagoda shape. The deflector is there to avoid pulsations.

    Additionally, the opening roof is heavier, which causes other non-aerodynamic losses.

    Tom
     
    #7 qbee42, Mar 19, 2012
(You must log in or sign up to post here.)