Why does the c get lower highway mpg than the Prius?

Discussion in 'Prius c Fuel Economy' started by ELODublin, Sep 25, 2013.

  1. ELODublin

    ELODublin Junior Member

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    Almost certainly buying a c this week. However, I must be lacking a basic understanding of how Toyota's hybrid system works. How can the c be rated at 2 mpg less than the Prius on the highway? It's smaller, and weighs much less.

    BTW a moment of silence for my 93 Camry. I hoped to buy historical vehicle plates in 2018, but a rod snapped and engines that old are hard to find, and expensive to buy and install. Incredibly, the engine starts and runs on 3 cylinders. It doesn't want to die....
     
  2. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    1) It has a worse co-efficient of drag than the liftback. The faster you go, the more aerodynamic drag is the primary drag.

    2) The HV battery is smaller, so less energy can be saved for the future.

    3) Toyota may be sand bagging their results. No one bitches when they do better than the EPA.
    2013 Toyota Prius MPG Reports | Fuelly
    2013 Toyota Prius C MPG Reports | Fuelly

    Weight is important when you are changing speed, but not so much in a steady state cruise.
     
  3. Reagan

    Reagan New Member

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    i'm getting a combined 53 mpg doing mostly 35 to 45 mph driving maybe 80 percent interstate,
     
  4. Prius NZ

    Prius NZ Junior Member

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    It is true that you get better high way consumption out of the Prius than the C. We have one of each and the C does marginally poorer mpg out of town. The Prius is aerodynamically better and the bigger electric motor and battery can contribute more during acceleration so the petrol engine doesn't have to work so hard, hence better consumption performance.
     
  5. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Is there a way to read this sentence so you are NOT doing 35 MPH on the Interstate? That scares me a lot, and would not be legal in MS.
     
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  6. Skylis A

    Skylis A Senior Member

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    I think that he's saying that 80% of his "combined" reported economy comes from interstate driving and the other 20% is from going 35-45 mph.

    Has anyone done a side-by-side test of "Prius" vs. "Prius C" fuel economy, at various highway speeds (e.g. 55 mph, 65 mph, 75 mph), to see by what margin the larger Prius wins out?
     
  7. Prius NZ

    Prius NZ Junior Member

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    Judging by the Toyota figures I would assume in order of efficiency it would go:
    1/ Prius
    2/ Prius C
    3/ Prius V

    The V comes out worse because it is less aerodynamic than the Prius and heavier while using the same engine setup.
     
  8. alfon

    alfon Senior Member

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    I believe the Prius engine is also bigger and perhaps more fuel efficient than the
    Prius C. At 60 MPH on level ground the engine is normally turning 1600 RPM or less.
    What is the RPM on the Prius C at 60 MPH level ground?

    I use a Scan Gauge II to check my RPM etc....
     
  9. minkus

    minkus Active Member

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    Partial explanation for the difference in coefficient of drag:
    AutoSpeed - Low Drag Car Aerodynamics

    Longer, more-tapered cars have lower coefficients of drag. Basically, the ideal shape is that of an airplane wing. The c is about a foot shorter than the liftback, which means the c doesn't separate the airflows going over the top and under the bottom of the car as long as the liftback does, which means that they form vortices instead of rejoining cleanly. The back of my c is almost constantly covered in crap, which would be a result of this. I'd imagine liftbacks get less crap accumulated on the backs of them.

    Here are some pictures/videos:
     
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  10. mahout

    mahout Active Member

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    Basically, its likely the smaller engine. While it weighs less and perhaps worse aero, the power required to move air out of the way at highway speeds requires 10 to 15 hp and that is a gretwe % of max power from the 1.5 liter engine compared to the 1.8 Lof the prius. The amount of air pushed aside is pretty close to the same for both cars hence the greater effort on the part of the C.
     
  11. mahout

    mahout Active Member

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    The aiurplane wing, unless turned upside down is not the most aero shape. Instead it is a teardrop rounded and tapered evenly along both sides and top with nearly flat bottom. Check the designs on sunracers and utah salt flat racers.
    Formula 1 racers have lots of those upside down wings to generate pushing the tires into the ground for better adhesion without the real weight penalty of centripetal forces throwing it off the side. Rules prevent a teardrop so all those wings and little fins are there tio make up for those losses.
    Bottom line is the C engine has to work harder than the Prius engine togo 60 mph. Work hader, use more fuel. Now if you'reclimbing a mountain that extra weight will put the Prius at less mpg than the C.
     
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