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Hypothetical Question: Optimum Driving Speeds

Discussion in 'Gen 2 Prius Main Forum' started by Mister Swigart, Mar 3, 2007.

  1. Mister Swigart

    Mister Swigart New Member

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    So, all things being equal (let's say flat ground, road surface, outdoor temperature, and no stop and go travel), what in your experience or knowledge would likely be the optimum speed for the Prius with respect to fuel economy? Oh, go ahead and venture a guess, but justify your response.
     
  2. TonyPSchaefer

    TonyPSchaefer Your Friendly Moderator
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    Flat ground, no traffic, decent outside air temperature: 44 MPH.

    All evidence is 2.5 years of anecdotal experience. I will hit and hold 44MPH as often as I possibly can. Not 43 and not 45.

    If speed is important, I'll go to 57MPH and hold it.

    I guess that if I think about it, there are reasons. For one, stealthing too much will drain the battery and then the ICE will kick in. And if you're going to have to maintain a speed while the ICE is running, anything below 40 seems inefficient to me. So that rules out speeds lower than 40MPH.

    On the other hand, at speeds greater than 55MPH, wind drag on the car starts affecting mileage. So that rules out speeds greater than 55MPH.

    Therefore, to identify "optimum" we find ourselves working in a speed band from 40MPH to 55MPH. Though I have no data to support it, I have found that if I can cruise at 44MPH for long stretches, I get very respectable mileage.

    So by now you might be wondering how I can say that I like driving at 57MPH while at the same time indicating that mileage diminishes at speeds above 55. I don't know.
     
  3. efusco

    efusco Moderator Emeritus
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    I don't have the graphs/data immediately available, but it's around 25mph....assuming all your conditions and sustained steady speed (ie non P&G)
     
  4. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(efusco @ Mar 3 2007, 06:36 AM) [snapback]399479[/snapback]</div>
    According to Wayne Brown's Hybrid Synergy Simulator it's between 20 and 21 mph. I don't know how close that is to real world, but the temperature makes a bigger difference that speed alone. Of course, wind and wind direction make dramatic differences. Going from 9 C to 39 C gives about a 12% mpg boost.
    It's no wonder we need to block our grills in the winter.

    Dave M.
     
  5. Mister Swigart

    Mister Swigart New Member

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    There are some very interesting comments here. I am fascinated by the results in two online articles, but neither one really explains the "gliding" technique beyond "let up on the gas." I think my Prius coasts fastest when I kick the shift over to neutral quickly and then back to drive when I drop to about 25. This is much faster than the coasting I get by simply letting up on the gas. Is that what they meant, do you think? Or is there some problem with using neutral?

    I felt the group would verify that it is below 45 miles per hour, but I'm surprised and alerted to try and take note of my results at 20-21 mph. I did not expect that.

    I am a bit concerned about holding up traffic with slow, and annoying experimentation, but there is plenty of open country roads in America, and I plan to use this knowledge when I tour.

    Have any of you had good results from using the "cruise control" off and on frequently. I'm experimenting with it in my own around town, stop and go driving.
     
  6. cwerdna

    cwerdna Senior Member

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    <div class='quotetop'>QUOTE(The Lone Ranger @ Mar 3 2007, 02:35 PM) [snapback]399617[/snapback]</div>
    See Advanced Techniques under http://www.hybridcars.com/gas-saving-tips/...yota-prius.html. Unfortunately, my commute isn't very conducive to this. I can only do this for a very short portion of it and only in the day for safety reasons.
     
  7. Woof

    Woof New Member

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    <div class='quotetop'>QUOTE(TonyPSchaefer @ Mar 3 2007, 08:57 AM) [snapback]399470[/snapback]</div>
    I'll agree with the above speed range of 40 mph to 57 mph. When I drive 57 mph to work I maximize my tank's overall fuel economy. During the month of January '07 with temperatures less than 35F, my brand new Prius tank fuel economy averaged 48 mpg. The instantaneous fuel economy indicator falls if the speed increases above the 55-57 mph range. In stop-and-go traffic, I can still maintain this economy if I travel as low as 40 mph. But, it's important to wisely use the regenerative break. To maximize fuel economy requires careful and thoughtful driving, like watching traffic patterns ahead of you.
     
  8. Mister Swigart

    Mister Swigart New Member

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    cwerdna,
    Thanks for this latest article. I have carefully read this, copied and pasted it to a new Word Document in two columns and will place this in my glove box so that my wife can read this, too. This article was the first I've seen to mention the use of neutral. I'm glad to see that I was intuiting this method of pulsing. I have been driving with the consumption screen on, and will look more at the generation screen. Thanks for posting this; it will really boost the learning curve for new drivers like me.
    TLR

    DC Woof,
    Although I look forward to touring in my new Touring car, I bought it mainly for the 12 mile round trip I drive every day. I am enjoying the challenge of paying attention to maximizing the mileage. I can afford the gas, but it's very engaging to "play this new game," and to see how it is changing the way I drive -- nothing like the muscle cars in my past, but good green fun, I must say, nonetheless!
    TLR
     
  9. cwerdna

    cwerdna Senior Member

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    <div class='quotetop'>QUOTE(The Lone Ranger @ Mar 3 2007, 04:36 PM) [snapback]399681[/snapback]</div>
    I noticed the mention of neutral too. I think that the whole part "engine on but not turning over and transmission in neutral" is ambiguous/wrong. I don't think it's a good idea to run in neutral and you really DON'T want the ICE running while gliding as it's consuming gas.

    BTW, I stumbled across/rediscovered http://www.toyota.com/html/hybridsynergyvi.../fall/mpgs.html. One of the marathoners talks about his technique at the bottom. There are more quotes at http://www.toyota.com/html/hybridsynergyvi...l/marathon.html.
     
  10. Mister Swigart

    Mister Swigart New Member

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    I am still uncertain about whether or not neutral was used in the record-setting method or not. I did a search and came up with one other comment about the use of neutral (see Odenton, Md)

    http://www.washingtonpost.com/wp-dyn/conte...6080301215.html

    There is a "black box" on board, and I think it could put me in double jeopardy if there ever was an accident (if it shows this).
    TLR.
     
  11. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    my optimum speed is 35 mph. i previously thought, the lower the better, but that does not seem to be the case.
     
  12. JimboK

    JimboK One owner, low mileage

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    <div class='quotetop'>QUOTE(The Lone Ranger @ Mar 3 2007, 07:36 PM) [snapback]399681[/snapback]</div>
    You'll probably enjoy CleanMPG. I encourage you to check it out.

    This thread from CleanMPG in particular might interest you. It describes pulse & glide as well as a higher-speed technique that some call "Warp Stealth" (a bit of a misnomer, but that's beside the point). While you're in that thread, explore the link in post #25 from Hobbit. Hobbit (a member here too) has done some fascinating research in optimal driving speeds and techniques, especially at higher speeds where P&G isn't practical. It's a bit technical, but it's a great read if you really want to understand the how and why of higher-speed FE.
     
  13. tomdeimos

    tomdeimos New Member

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    My best mpg is at 35 also.

    I expect this is near optimum since going faster prevents electric ice off mode, at least over 42. Also adds drag. Going slower makes for inefficient ice runs even with load to charge the battery.

    I can't drive 35 enough around here to know what my mpg would be but I expect it would be around 80 mpg if I was where I could do it. I have sustained over 75 mpg for some extended periods going around 39 mph.

    I think this optimum may depend on having rolling hills. If everything was flat then a different speed might be optimum where engine was kept running. So then maybe 43 mph would be good. But with small hills clearly keeping engine going is bad on the down grades.

    With pulse and glide added then pulsing between 5 mph and 35 mph might make sense. Or with hills you need to adjust this so engine is on for uphill and off for downhill.

    So my numbers may be off a bit but clearly there are at least 3 optimums depending on terrain and driving steady vs pulsing.
     
  14. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(The Lone Ranger @ Mar 3 2007, 02:35 PM) [snapback]399617[/snapback]</div>
    What were your results at 20-21 mph, and what had you expected?

    Dave M.
     
  15. Mister Swigart

    Mister Swigart New Member

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    Edited: I had a post here, but decided it would get lost in here and somewhat changes the topic. So it comes under its own topic heading. See:
    My Method: Pulse-Cruise/Neutral-Drive-Glide/Resume
     
  16. KV55

    KV55 Member

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    I try to iron out the peaks and troughs on a journey and aim to drive at the average speed for that journey. My weekend commute takes me around 2 hours 20 minutes over 86 miles of A roads. My average is 37mph and my zen is get my top speed as close to my average as possible. The hills throw in an added dimension, the steep short hills are good for going up and the long gradual hills are good for going down.

    My typical fuel use is 65mpg (UK) with a best in the summer of 72mpg. I used the minor roads for that journey and averaged just 29mph. My target is to do the whole 86 miles from a cold start on one gallon, a hard target but fun. It's acceleration that uses the fuel and keeping a steady speed into a headwind or up a hill is the equivalent of accelerating.
     
  17. PriusWise

    PriusWise New Member

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    I get the absolute best MPG between 1 and 4 mph, using pulse and glide, with the engine off and my hands pressing on the hatchback instead of my foot pressing on the gas pedal. When I get tired of pushing, I let the car coast to 1 mph and then begin pushing before the car comes to a full stop to avoid start up inertia and cohesion of the wheel bearing grease molecules. Occasionally, when near large intersections, someone will jump out of their car to help me get across several lanes quickly. Thats a nice bonus. I find that I can avoid oil changes entirely this way. I'm thinking of having the gas engine and battery removed next week to lighten the car up. Of course I will need to figure in the cost of having the speakers moved outside of the car so that I can hear them. It's complicated.

    Dan, 3rd gen from the sun