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Better mpg at 60-65 mph than at 55 - 60 mph

Discussion in 'Gen 3 Prius Fuel Economy' started by HelloMyPrius, Mar 1, 2010.

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  1. ken1784

    ken1784 SuperMID designer

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    We know Prius is clever enough to trace most efficient engine torque and engine rpm combination to meet the driver's power requirement as shown at engine efficiency map.

    Of cause, the engine has a sweet spot (220 g/kWh) and the worse point is 230 g/kWh.
    But, the efficiency difference is only less than 5%.
    OTOH, the air drag difference between 55 mph and 65 mph is approx 40%.
    Therefore, I believe the air drag is affected more than engine efficiency for the 55 - 65 mph band mpg numbers.

    Ken@Japan

    [​IMG]
     
    #61 ken1784, Mar 11, 2010
  2. Tande

    Tande Active Member

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    We are talking about Gen.III correct?...Then, Yep, Me/Too....Have tried it many times (all interstate driving); no doubt in my mind (don't ask me to "Prove" it):nod:
     
    #62 Tande, Mar 12, 2010
    Threej likes this.
  3. HelloMyPrius

    HelloMyPrius New Member

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    Bob, great information. How is the slope of the run? I am wondering about the effect of terrain on your two runs in opposite directions. In a way, do you assume some kind of symmetry. That is net effect of gain in efficiency down hill at 60 miles per hour plus the loss in efficiency up hill at 60 miles per hour vs. net effect of gain in efficiency down hill at 70 mph plus the loss of efficiency up hill at 70 mph. Maybe it is not a factor because the road you test on is very flat. My personal experience is that at high speed, MPG is greatly affected the terrain. Will your test unfairly biased against MPG at high speed because gain in efficiency in downhill at 70 mph doesn't offset as much loss of efficiency in uphill at 70 mph as it would at 60 mph?

    Just a thought.
     
    #63 HelloMyPrius, Mar 13, 2010
  4. HelloMyPrius

    HelloMyPrius New Member

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    Ken,

    I would agree with your conclusion if air drag is a pre-dominant resistance. There are some posts on the net suggest that
    I don't know if this is true or not. With more aerodynamic design of Prius, this limit may be around 65 mph. This could be another factor that creates an inflection point around 60 mph per our experience because after that air resistance goes up as v^2 and reduce MPG.
     
    #64 HelloMyPrius, Mar 13, 2010
  5. HelloMyPrius

    HelloMyPrius New Member

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    After I am done tracking my current tank MPG. I will do some experiment during my commute route.
     
    #65 HelloMyPrius, Mar 13, 2010
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