Wondered about my Prius mileage but then

Discussion in 'Gen 3 Prius Fuel Economy' started by jburns, Jun 17, 2011.

  1. jburns

    jburns Senior Senior Member

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    I have had my Gen III for almost 2 years and have never had a tank average 50 mpg. Always in the upper 40s summer and lower 40s winter. I live near 70 mph interstates so I usually run 75 to 80 mph when on a long run. I also just drive the car and outside of a time or two don't go out of my way to inflate my mileage. All in all I'm happy with what I get considering my circumstances but still, based on all the mileage claims here, wondered if maybe my car might have a minor issue.

    This week however I had to follow a school activity bus from near my house to Charlotte, NC. A 150 mile round trip on I85. In NC activity buses are governed at 55 mph. So off we went down I85 at a speed I haven't driven since I was riding bicycles 50 years ago. Activity buses also gradually lose speed on any upgrade which is also good technique for mileage. I have have to tell you that there is nothing wrong with my car. The 75 mile trip south I averaged 78.5 mpg. Coming home 72.5. Total for trip 75.5 mpg. I was truly impressed.

    I won't be changing my normal driving method but I don't think I have to worry about something being wrong with my car.


    EDIT: The mileage numbers are Prius computer figures. I know the actual will be a few MPGs less.
     
  2. usbseawolf2000

    usbseawolf2000 HSD PhD

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    Aero drag is a bitch. Engineers have done what can be done with 0.25 Cd.

    See the table below. There is one thing the driver (you) can do. :D

    Column 1
    0 MPH Watt hours per mile % of Energy used to Overcome Aerodynamic Drag
    1 40 152.8 Wh 29.8%
    2 45 181.3 Wh 31.9%
    3 50 190.8 Wh 37.3%
    4 55 202.9 Wh 42.5%
    5 60 215.5 Wh 47.6%
    6 65 233.4 Wh 51.6%
    7 70 250.3 Wh 55.8%
    8 75 268.5 Wh 59.7%
    9 80 287.8 Wh 63.4%


    Source
     
  3. cwerdna

    cwerdna Senior Member

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  4. SpikeVFR

    SpikeVFR New Member

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    How and where you drive can have a HUGE impact. In the 7 years I have owned my car, I have, unfortunately had several jobs with widely varying routes. My mileage has changed greatly.
    1) for the 1st 4.5 years I owned the car, my commute was 25 miles each way, usually in moderate to heavy traffic. Got 45-50 in winter, and 50-55 in summer.
    2) then a 40 mile commute for 4 months, almost all highway, but off times, so not much traffic. 50 MPG
    3) then 8 mile commute for 10 months, depending on route, was about half highway or no highway, mid to high 30's
    4) now 30 miles, mid 40's, for the last 4 months, but just found out my catalytic converter is bad, so that maybe dragging it down
     
  5. J5A

    J5A Active Member

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    Wondering if any drafting occured which resulted in + mpgs.
     
  6. mad-dog-one

    mad-dog-one Prius Enthusiast

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    In addition to dramatic improvement in fuel economy, slowing down can also help moderate your blood pressure and can provide the opportunity to "smell the roses."
     
  7. cwerdna

    cwerdna Senior Member

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    Yep. My lifetime average when I had a much longer commute in CA, about 2/3 of it by time on the highway was ~46 mpg.

    Now w/my colder climate, very short city drives and a bunch of uphill to start (and downhill that frequently causess my HV battery to get "full" (to 77+% SoC that the ICE starts up), I'm lucky to even get 40 mpg.
     
  8. jburns

    jburns Senior Senior Member

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    no. I stayed well back. Would have been like trying to draft a covered wagon. :p
     
  9. jburns

    jburns Senior Senior Member

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    I lived and drove in Germany in the late 60s. What lowers your blood pressure is not having speed limits, so you're not worried there is a cop behind every tree. As far as the flowers, its more likely I would smell the fertilizer. :)
     
  10. adamace1

    adamace1 Senior Member

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    I think you figuired it all out. I drive alot in charlotte, I 77 speed limit is 55 so i go 55 to 65 with traffic. And i get some city driving in there too. At the high speeds your driving i would get in the mid 40's. i get over 50mpg going a max of 65, bot alot of 55-35 mph driving thats gets me 50-54mpg.
     
  11. SpikeVFR

    SpikeVFR New Member

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    Not for me, no. Hate being behind a vehicle I cant' see thru. Not worth 3 MPG to me to try to stay in behind a truck or close enough to a car to get the drafting effect at the possible expense of rear ending someone.

     
  12. GSW

    GSW PRIUS POWER

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    +1, or try to dodge a blown tire if your drafting a large truck.
     
  13. sipnfuel

    sipnfuel New Member

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    Even staying a few car lengths back really results in a boost, so I think your results still show the effects of drafting.

    You aren't drafting like a NASCAR driver does with less than a car length, but even at 10-15 car lengths you can notice the effects.

    Here are the results of the Mythbusters test.

    Reduction in fuel consumption driving behind a semi trailer at 55 mph, per distance trailed

    100 ft (30 m) 11%
    50 ft (15 m) 20%
    20 ft (6 m) 27%
    10 ft (3 m) 39%
    2 ft (1 m) 28%
     
  14. Insight-I Owner

    Insight-I Owner 2006 Insight-I MT + 2011 Prius

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    The Prius is just under 15 feet long so:

    100 ft (30 m) 11% is 6-7 lengths back
    50 ft (15 m) 20% is about 3 lengths back
    20 ft (6 m) 27% is about 1 length back
    10 ft (3 m) 39% is 2/3 length back
    2 ft (1 m) 28% is 1/7 length back

    IOW, closer than you would think.

    Incidentally, 100 feet is a tad over 1 second at 60mph (88fps), less than that at higher speeds. Good reflexes?? Basically, if you are drafting at a distance close enough to have a significant draft effect you are dangerously close. If you are at a safe distance, there is very little effect.

    I tried drafting a truck once and discovered that any sort of terrain strategy was impossible, and constantly reacting to what the truck was doing meant that I couldn't drive efficiently.

    I found that I could do a lot better mpg wise by NOT drafting trucks: 67.7mpg on the display today over 140 miles from Boston to here, a good part of it with the AC on set at 75 degrees. Figure 3-6% less when corrected for the display error.
     
  15. mmcdonal

    mmcdonal Active Member

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    Actually, well back is almost as good. Trying to stay too close can adversely affect mileage is you have to speed up and slow down to keep your gap. But staying back you were probably still in dirty air, so got some benefit - unless it was more than a 100 yards or so.
     
  16. SpikeVFR

    SpikeVFR New Member

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    Did run into a piece of sheetrock a couple of weeks ago, like 3' x 4' left nasty scrapes in my hood.:mad:

     
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