The Sweet Spot on Highway Mileage.

Discussion in 'Gen 2 Prius Fuel Economy' started by equationer, Sep 25, 2019.

  1. equationer

    equationer New Member

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    As a owner of Gen2 2005 Prius currently at 205K miles and based in UK. I am not a hypermiling freak , I drive normally albeit a little conservative. I would like to open a discussion on Highway Mileage after I noticed something peculiar.

    I have come to realise that the sweet spot for Highway Mileage for this car is at about 55MPH. I noticed it when we had a traffic at Motorway mainatiance where we are to drive at speed of 50MPH for about 5 miles. The speed is mainatianed constant throughout 5 miles and I noticed the MPG I got is surprisingly 65MPG. When I went back to 70MPG it drastically dropped to below 50MPG. I used to always take the right Lane and drive at 75 to 80MPH or even above for maximising fuel efficiency and used to complain on 40MPG it got. From then on I realised the sweet spot and always took the Dual Carraigeways where ever possible to take 50MPH route instead.
    I am not complaining about city mileage as it is sensible enough to know that Prius and any hybrid always saves you great on the city. So I am trying not to discuss City Mileage here.

    Has anyone ever tried doing it with their Prius . I am curious to know the more powerful 1.8L on Gen 3 or above would give you a higher sweet spot probably at 65MPH.

    And of course the new Corolla Hybrids with number of option from 1.2L turbo, 1.8L and 2.0L. And here's my little theory - since Corolla being lighter than Prius , the same 1.8L can push the sweet spot to the UK standard 70MPH Motorway. And for some of us who tend to take right Lane to cruise at 80MPH or above , the Corolla 2.0L might save you better at that speed.

    And as we can imagine the Turbos always gets you more power on less fuel, the new Corolla Hybrids has the option too, the 1.2L turbo Hybrid. As funny as it may sound I was playing with this idea in my head few months ago , and Toyota has all three options now in their Corolla Hybrids. Anyone with the new Corolla Hybrids please exercise on your data. I myself am longing to get the 1.2 L just to drive this curiosity of mine.

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  2. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    55 is a near-universal sweet spot given that we are all driving through air of similar density.

    Some designs can stretch the sweet spot a little, but it’s mostly down to aerodynamics.
     
  3. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    I drove my Gen 2 at 61 MPH a great deal, it seemed to get good mileage and not slow anyone down.

    My 1.8l v does not take as sharp a hit in MPG with more MPH, but 61 MPH is still a good impression of ideal.
     
  4. MickyMatter

    MickyMatter Active Member

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    A dutchman simulated this consumption map chart with the parameters as stated there.

    https://www.john2211.nl/Spreadsheets/2004%20Prius%20-%20Palm%20THS2%20Simulation.htm

    But instead of mileage it shows the consumption in liters per 100 kilometers, which is usual here in Europe. So less is better.
    60 km/h = 37 mph.
    3,2 l/100 km = 73,5 mpg, which I've reached sometimes. Mostly I'm driving with about 4,5 l/100 km or 52,3 mpg on my daily roads.
    On autobahn (I'm living in Germany.) I often drive at 170 km/h or 106 mph (when there's no traffic jam) with then roughly about 8 l/100 km or 30 mpg. Screenshot_20190925-163022_Firefox.jpg

    SM-G950F ?
     
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  5. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    65 kph is 40 MPH
    28C is 82F
     
  6. Mendel Leisk

    Mendel Leisk Titanic Social Director

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    Sweet spot implies there's some plateau in the graph of mpg vs speed? And you can run out to the right end of that plateau, get good mpg with increased speed all the way to the edge? I don't know, looks like a pretty uniform correlation to me:

    Updated MPG vs MPH chart | PriusChat

    I just stay right and as slow as acceptable.
     
  7. equationer

    equationer New Member

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    Except in my Gen 2 Prius: above the 55MPH, the MPG tends to go up drastically to below 50MPH (@70 MPH) and to 40MPG (@ 80MPH). The Chart sort of will look like a upward facing paraboloid instead.


    Posted via the PriusChat mobile app.
     
  8. dolj

    dolj Senior Member

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    Did you mean go down?

    Remember that MPG is not a linear scale but exponential, so while it appears to go down drastically as your speed increases, changes from 70 MPG to 50 MPG is not much and certainly nowhere as much as 40 MPG to 20 MPG (both a 20 MPG difference).

    One other factor to remember, discussion of MPG on either side of the Atlantic, you need to differentiate between imperial and US gallons. and then the discussion gets really messy. I'd recommend that you choose one or the other unit (i. e. either all use MPG (UK) or all use MPG (US)), and use it exclusively in the discussion. So, sorry, but one of the camps will have to convert to the other's in order to have a sensible discussion.
     
    #8 dolj, Sep 26, 2019
    Last edited: Sep 26, 2019
  9. equationer

    equationer New Member

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    Sorry I actually meant when I get to the 70MPH Motorway speed, the MPG drops down to below 50MPG. I have never gotten 70MPG.

    Posted via the PriusChat mobile app.
     
  10. equationer

    equationer New Member

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    And yes I am referring to the imperial MPG.
    My measurent were taken on the basis of Prius dash screen information.
    And what I did was reset. I resetted before I drove 5 miles @ 50MPH which gave me 65 MPG. Then I reset it again to measure on about 10 miles @ 70MPH which gave 49.** MPG.




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  11. dolj

    dolj Senior Member

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    For the benefit of all:

    US:
    I reset before I drove 5 miles @ 50MPH which gave me 54.1 MPG (US). Then I reset it again to measure on about 10 miles @ 70MPH which gave 40.8 MPG (US).

    Metric:
    I reset before I drove 8 km @ 80 km/h which gave me 4.35 L/100 km. Then I reset it again to measure on about 16 km @ 113 km/h which gave 5.77 L/100 km.
     
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  12. equationer

    equationer New Member

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    Thanks. I appreciate it.
     
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  13. will the engineer

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    Hmm with my gen, driving 80 mphs gives me better mpgs

    60+

    Couldn't figure out why the system is outputting that reading. I doubt its wrong, but no idea why
     
  14. equationer

    equationer New Member

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    You have the latest Prius Prime and equipped with a larger engine capacity 1.8L as compared to mine which is a 1.5L.
    And Prius Prime has a larger electric motors that will assist even at higher speed. With mine, the electric motor is pretty much idle after 40MPH.
    Also are you mentioning your average MPGs combined city and highway. I was just focusing on the Highway mileage , constant 70MPH over 10+miles. Next time when you get into interstate highways or motorways try resetting the dash and read what it says at the end of the 10miles trip.
     
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  15. equationer

    equationer New Member

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    Its been a week my car gave P0016 error. May be the timing chain.
    Anyway I am driving it as it is.

    Just yesterday drove 5 miles constant @50MPH in Cruise Control Mode and actually got 75 MPG. -- UK. (US- 60MPG).
    I was driving alone with no passenger and no luggage. The road was wet with recent heavy rain and temp about 18C(64F).

    Just yesterday had to drive very far using the Motorway M4. From Junction 11 - junction 13 had to drive through 50MPH highway mainatiance traffic. Reset the dash, put it on cruise 51MPH , and BAM after 5 miles my mileage was 75MPG.

    Then I drove 50miles at motorway @70 MPH cruise , my mileage was 52 MPG(US 43MPG).

    I will have timing chain replaced soon. And see how it does again.





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