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Uphill vs. downhill makes the biggest difference

Discussion in 'Gen III 2010+ Prius Fuel Economy' started by PriusRos, Aug 29, 2009.

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  1. PriusRos

    PriusRos A Fairly Senior Member

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    Let me start by saying that I am still under the first 1,000 miles in my new Gen III so the car might not be fully "broken in" (although I'm not sure that I believe in a break-in period for the car, only for the driver) but I am finding that my experience so far is similar to Consumer Reports' findings and my FE is not showing much of an improvement over my Gen II.

    My daily commute is a 4-5 mile drive (depending on which route I take) to and from the Metro station. In the morning, the first mile is mainly uphill, and then it's more downhill for the rest of the way. In the evening, it's not exactly reversed because I usually take a slightly different route, the shorter one, but it still involves about 2-3 miles mainly uphill, followed by a mile downhill. I'm not talking mountainous terrain or San-Francisco-style hills - just slight inclines up and down. There are a lot of lights on both routes, but it's busier and I usually have to stop more frequently in the morning.

    Up to now I hadn't paid much attention to whether the mileage was better in one direction vs. the other. All I know is my overall average mpg (including longer highway trips) was only around 44mpg in my Gen II. For my Gen III, I've had two fill-ups so far, and am averaging around 45.

    Anyway, for the past few days I've been resetting my Trip B meter at the beginning of each trip in the morning and the evening. I have found that my for morning commute, which is more downhill, I can get 47-51mpg on the display. The last part of the drive consists of climbing ramps in the garage in EV mode. However, on my evening trip, no matter how hard I try, I am only getting 36-40 mpg! That's a big difference, and would account for my overall mediocre FE.

    I have also observed this for longer highway trips (about 30 miles each way). In one direction, the displayed showed 63mpg. However, on the return trip, it went down to 55mpg (this was the average for both directions because I hadn't reset the meter for the return trip). Again, I believe the difference was due to the the topography. Sometimes I can't even tell whether I'm going uphill or downhill, except by looking at the mpg display and knowing how hard I am pressing the gas pedal.

    P.S. I realize that my topic title could be considered "No-duh", but I haven't seen a specific thread on this topic before!
  2. bwilson4web

    bwilson4web 03 and 10 Prius

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    For what is worth:
    [​IMG]

    I'm a great believer in route planning. Have you used Google Earth or Google maps to find alternate routes that may allow slower speeds ascending the hill(s)?

    It would be especially helpful if you could give some Google Earth coordinates of your route (we don't need your home address but say a corner.) Then start a daily log from a reset trip meter. This may give some clues to how to approach a hilly commute.

    Thanks,
    Bob Wilson
  3. PriusRos

    PriusRos A Fairly Senior Member

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    Thanks, Bob. I've varied my route for precisely this reason. I usually use the longer route in the morning because I found that I was getting better mpg than I was on the shorter route -- both because it has slightly longer time to warm up and because there is more downhill. However, coming home, there is an even longer uphill climb at the beginning of the trip if I use that route, so I take the shorter one.

    I'm will probably stay with the morning route since that seems to be doing well mpg-wise and actually is slightly faster although it's longer because there's more main road, but there are a few other variations I can try for my evening trip home and will keep a log of the results.
  4. DetPrius

    DetPrius Active Member

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    I have observed the same thing over a longer drive. I work from home nearly 100% of the time but a few weeks had to go into to work for the first time with my 2010 Prius. My mileage on the 33 mile drive going in was very good, as in something like 64 mpg on the car. I reset the B trip meter for the drive home and was well under 60. I also felt on the way home I was doing more uphill stretches than on the way in. I had never noticed this in my previous car when I drove in 5 days a week. I looked up the elevation of the "from" and "to" locations and found they were almost 600 feet apart in elevation. This is only from one observation but I believe the elevation difference can add up quickly. It probably affects non-hybrids as well but not as much as the hybrid since it has been optimized to maximize mileage and anything working against this goal is felt.
  5. Rokeby

    Rokeby Member

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    PriusRos,

    You have come upon two of the fundamental truths underlying getting
    really good FE:
    * route and topography make a difference. Sub truth; out-going
    routes and returning routes for best FE are usually different. Good hills
    have short, steep climbs and long, low-angle declines.
    * one way FE figures are not truly indicative of overall FE. You have to
    look at the round trip to get meaningful numbers.



    I am speaking from Gen II experience, but I believe it is relevant to
    the Gen III in this situation.

    Recognizing that your home-going trip is a long uphill climb leads to
    the beginnings of bringing your MPG numbers up. That said, pulling
    your car up the garage ramps in EV probably has a significant
    contribution to your low going-home FE. The car draws heavily on
    power from the HV battery during the start-up engine/catalytic
    converter warm-up period. It can easily result in SOC falling 10 or
    15%. Rolling down the ramps in regen does not recoup this drop. You
    may also notice that even though you are in regen, the engine is
    running, even though it is making no contribution to the movement of
    the car and wasting gas.

    Finally, it will take quite a few miles to recover the SOC. During this
    time the Power Split Device PSD will be diverting power through MG2
    rather than directly to the wheels for the most efficient propulsion.

    Just something to consider as you find what works best in your
    specific driving environment.
  6. PriusRos

    PriusRos A Fairly Senior Member

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    That's interesting. Indeed I have noticed that for my evening trip, starting with going down the ramps, I am using gas even though the car could just roll under gravity (and showing around 11mpg) and I could never understand why it's doing that. I'll stop turning on EV in the morning and see whether that makes a difference in the evening. Thanks for the tip.
  7. Rokeby

    Rokeby Member

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    PriusRos,

    It may be better to come down the ramps in EV! :eek:

    This is counterintuitive, but when you consider how the HSD works it
    makes enough sense at least to give it a try.

    Disclaimer: my experience is in my Gen II with after-market EV
    switch. I hope it is relevant here.

    As soon as the ICE starts, the HSD's first priority is to get the car
    operating to produce minimum polution. It does this by running the ICE
    rich which ultimtely leads to quick warm-up of the catalytic converter.
    So, like it or not, the first minutes and miles produce very low MPGs.
    One way to work with this unpleasant truth is to set things up so that
    you are at least making some mileage while the MPG numbers are
    low.

    I don't know if there is a discretionary use EV switch in the Gen III.
    If there is, engaging EV mode to get out of the garage will suppress the
    engine coming on and you won't be using either fuel or SOC and your MPGs
    don't take as big a hit! :rockon: It works for me anyway.

    As soon as you get out of the garage, drop out of EV so you don't run
    down the SOC and incur the attendant recovery costs.
  8. PeteJE

    PeteJE Junior Member

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    Thanks for sharing, I am having very similar observations - great mileage legs and horrible mileage legs. Hills are work for this car. I have a gentle long uphill to the foothills where I live (1-2 miles up up up). The top of the HSI, the last pixels where I can keep the ECO lit before the power area, yeilds me very very slow acceleration and speed. There are 2-3 stop signs and trying to keep ECO lit can only get me (very slowly) to maybe 16 - 20 mph in this 30 mph zone. I do it if no one in behind, but that is rare.

    Is it better to just use the gas to get up to the speed limit in the pwr area on HSI then back off to maintain, or to do the long, slow acceleration whe ECO lit?

    Can anyone shed more light on the pwr area of the HSI? What does that tell us other than lots of engine work?

    I am averaging 46.8 mpg over the life (only 750 miles total - basically break in period) and now 54 mpg on my last tank reset that includes a couple of work round trips. This, honestly, has been a combo of learning technique, working hard at it, and totally blowing it off for traffic and habit at times. To me, it seems the car will get exactly as advertised on the EPA sticker - for folks like me without consistent great technique (the general public).

    I had one work round trip at 60 mpg - but more miles on that trip meter quickly averaged that down. This one trip had very little traffic that forced me to worry about being too slow, or under the speed limit, etc.

    My best mileage seems to come on the long, gentle freeway downgrades where I go to glide mode (no HSI bar at all).

    I just share for anecdotal data points - I am anxious to learn and slowly grow my MPG. It is funny to become obsessed with MPG up at this level after driving a 5.2 Jeep V8 at 12 mpg for so long. This is the best!
  9. PeteJE

    PeteJE Junior Member

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    There is an EV switch/mode, but discretionary is up to the car, not the driver. There are many conditions where the car does not allow it - one of them is when cold. I can never get it to work first thing after a long cooling off period.



  10. bwilson4web

    bwilson4web 03 and 10 Prius

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    This is an area of interest for many of us who have contributed to Hobbit's thread. I've been able to map the power generated at 50%, 75% and 100% but I don't have the instrumentation to map the field, brake specific fuel consumption. This is coming but not here, yet.

    There are some other aspects that have me wondering what is going on. For example, my "off the lot" performance was significantly better than recent numbers. Some of this may be lubricant related and I should have some data on that in about a month. Some may also be due to traction battery settling, a phenomena not yet throughly understood. It is an interesting time to have a new Prius.

    Bob Wilson
  11. PriusRos

    PriusRos A Fairly Senior Member

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    I've tried -- it won't go into EV on start-up. I could be mistaken, but I don't think EV will work when you first start up regardless of how much charge the battery has.
  12. Rokeby

    Rokeby Member

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    Well, there you have it. General Gen II knowledge doesn't always map
    across to the Gen III. I hope that I haven't wasted your time.

    As Bob Wilson has pointed out, you are in the first days of discovering
    the minutiae of how the Gen III operating algorithms work. In all the
    years of the Gen II thre are still many questions and mysteries despite
    the work of Bob, Hobbit, et al.

    To all the Gen III explorers, investigators, and de-mystifiers, keep up
    the good work.
  13. PeteJE

    PeteJE Junior Member

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    No waste of time, I like all the help and understanding I can get. There will be many here trying to learn; some stuff old news to most others here, and some stuff new to Gen III.

    TeamPrius showed the demographics of sales here.... lots of first time hybrid owners with the gen III (I am one).




  14. PriusRos

    PriusRos A Fairly Senior Member

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    Not a waste of time at all. You had an idea that made sense ... except that the Gen III EV switch is very picky about when it will let one use it!
  15. EternityInBlack

    EternityInBlack Junior Member

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    Much like the OP, I live in an area that's very hilly - in both the side-streets and the highways. I've managed to increase my mpg from what I started with at the dealership (40mpg) and have it hover around 41.3-41.9mpg. The constant need for acceleration on the uphill climb is what I've discovered that drops the mpg. Also, it doesn't help that the on-ramp to the freeway heading to work is a long uphill climb.

    I'm going to try and see if I can increase my mpg today by avoiding the freeway altogether and using the side streets heading home as the uphill/downhill isn't as bad. I'm curious to see how the mpg would react to this change.
  16. SR1227

    SR1227 New Member

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    EV can work at start up, if you have enough charge. The car will need a few secs to initialize before the EV will engage. So I just keep pressing the button every sec or so until it lights up. Just be sure to engage it before the ICE starts warming up. No going back after that happens. Then, you just have to make sure you're going less than 10mph on those garage ramps. It will kick you out of EV if you go over 10, although I haven't tested that limit with a no-gas free-roll condition.
    1 person likes this.
  17. LoraJ

    LoraJ New Member

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    Going to work today, which has a few hills going up including a pretty good sized one (for a city area), I got 43mpg. Coming home we got 65mpg.
  18. PriusRos

    PriusRos A Fairly Senior Member

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    The other thing you'll find is that a low mpg for one stretch brings the average down much faster and lower than a high mpg over a similar distance brings it up! Darn those mathematical laws!
  19. LoraJ

    LoraJ New Member

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    Yup!
    My mpg for the tank is finally out of the 30's and is now 42. Tomorrow I am going to track our whole commute together.
  20. Kapena Gary

    Kapena Gary New Member

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    This is a very good thread. I have about 1,500 miles so far and usually drive short distances (with AC on almost always) and notice that because of the ICE running to heat up the catalytic converter my MGP is fairly low for half the trip which so far results in around 45-49 MPG.

    But on longer trips, like 100 to the airport, I can easily get 52-55 MPG. I really think the warm really hurts MPG but once you get beyond the warm up period great milage is possible.

    PS - First Prius, absolutley love it. :)

    And the members here are so loaded with great information. Thanks to all.
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