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Which, if either, gets better mileage.

Discussion in 'Gen 3 Prius Fuel Economy' started by thbjr, Mar 1, 2011.

  1. thbjr

    thbjr Member

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    OK, I understand the best mileage is gotten when the car never has to stop, but having said that and setting certain criteria for the question, which driving style would get the better mileage?
    For this questions purpose, lets say we are on a closed track, straight line driving on level ground. Also, for the sake of setting up the question, it will take 1/4 mile to accelerate to 45 MPH with the HSI bar in the top 10% below the Power range (max acceleration efficiency) and 1/2 mile to glide back down to 5 MPH then back to 45 MPG cycle (with the transmission engaged, below 5 MPH requires braking) for the P&G parameters. If these P&G ranges aren't realistic enough, substitute, but it sets up the question. For the other part of the question, same 1/4 mile to accelerate to 45 MPH, but the glide is only down to 40 MPH before accelerating back to 45 MPH for the P&G parameters and the final 1/2 mile glide would be from 45 to 5 MPH to complete the course. Since the first set of parameters nicely fits into a 3 mile section, we'll use that number.
    So my question is, over a 3 mile test, would the greater fuel efficiency be with the extreme of 45 to 5 MPH P&G cycles or the almost constant speed of 45 to 40 MPH P&G cycles? Would they be the same?:confused:
    Thanks for your input.
    Tom
     
    #1 thbjr, Mar 1, 2011
  2. spiderman

    spiderman wretched

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    I think it would take a lot longer distance to notice any difference. But theoretically, the P&G cycle should come out ahead.

    Have a good day Tom!
     
    #2 spiderman, Mar 1, 2011
  3. SageBrush

    SageBrush Senior Member

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    Average slower speed means average lower air resistance.
    Just do not waste the advantage by getting bored and turning on the radio ;)
     
    #3 SageBrush, Mar 1, 2011
  4. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Concur.
    IF you have the real estate to make use of P&G.
     
    #4 ETC(SS), Mar 1, 2011
  5. qbee42

    qbee42 My other car is a boat

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    Both situations posed by the OP are for P&G, which renders the previous replies about P&G pointless. The OP wants to know *which* P&G will work best, not whether P&G works better than normal driving.

    SageBrush gave the proper answer, which is that the 5 to 45 mph cycle will produce better mileage because of the lower average speed.

    Tom
     
    #5 qbee42, Mar 1, 2011
    1 person likes this.
  6. PaulHS

    PaulHS Member

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    Tom, I realize you are looking for others' opinions but, based on your Fuelly numbers, you are probably the one who can best answer your question.

    My initial thought was that the long P&G cycle would be more efficient. In fact, that's how I generally drive whenever possible. It seems to have served me well. But, as Spidey has said, theoretically the short P&G should be more efficient. Better conservation of momentum...
     
    #6 PaulHS, Mar 1, 2011
  7. thbjr

    thbjr Member

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    Paul, qbee and Sage, all understand the question I was really getting at. Is it better to conserve motion with short P&G cycles or have a slower avg MPH with the long P&G cycles? I agree that 3 miles is not a long distance, I just used it because it would cover 4 long P&G cycles, in the scenerio perfectly. Could be 30 miles just as well.
    My personal thought leans towards the long cycles as well, but then I started thinking about conservation of motion when I was on the freeway, CC set at 58MPH and getting 60+ MPG and thus the question.
     
    #7 thbjr, Mar 1, 2011
  8. fuzzy1

    fuzzy1 Senior Member

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    I'm missing something. What does conservation of momentum have to do with P&G efficiency? When folks talk about conserving momentum in other situations, they are really talking about cutting unnecessary braking and other friction.

    I vote with qbee, the lower average speed of the longer cycle will reduce air friction loss. Plus, the fewer ICE starts and stops should cut some transition losses.
     
    #8 fuzzy1, Mar 1, 2011
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