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SuperHighway Gliding with the ICE in Neutral (NICE)

Discussion in 'Gen 3 Prius Fuel Economy' started by walter Lee, Nov 27, 2011.

  1. walter Lee

    walter Lee Hypermiling Padawan

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    I was experimenting with NICE at over 50 mph yesterday
    (I270 from Rockville,MD to I495 to TysonsCorner,VA;
    about 24 miles/60minute trip; temperature > 60F).

    I found that on a mild downhill grade ( < 15 degrees down,
    > 7 degrees down) and a long enough stretch of road
    ( > .2 miles), a warmed up engine ( Fwt > 160F, 30 minutes
    on), a HV Battery with a SOC > 50%, and over inflated tires
    ( 50psi front/ 48 psi rear) -- then on clear sunny day with
    a dry smooth road surface (whentraffic allowed it) - I
    could maintain a speed greater than 50 mph in Neutral
    without using any battery power or gas! The scangauge
    trip mileage indicator (AVG) also indicated that switching
    from Drive to Neutral on the downhills seem to help
    raise the highway fuel efficiency ( 70 mpg southbound
    overall 66 mpg northbound overall, with the hwy speed
    from 50mph to 60 mph) - I'm sure the lower speeds
    helped keep the MPGs up but on cruise control at 55
    mph - I was expecting something around 63 mph not 66mph
    or 70 mph - So I'm thinking this technique is good for a
    3mpg to 7 mpg boast in mpgs.
     
    #1 walter Lee, Nov 27, 2011
  2. DetPrius

    DetPrius Active Member

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    I believe you run the risk of over-spinning MG1 by coasting too fast in Neutral, but I'm sure someone else will be able to confirm or refute this.
     
    #2 DetPrius, Nov 27, 2011
  3. tumbleweed

    tumbleweed Senior Member

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    #3 tumbleweed, Nov 27, 2011
  4. firepa63

    firepa63 Former Prius Owner

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    Driving in neutral is also illegal in some states.
     
    #4 firepa63, Nov 27, 2011
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  5. SageBrush

    SageBrush Senior Member

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    Optimizing HSD: good
    Circumventing HSD: bad

    Leave the car in 'drive'
     
    #5 SageBrush, Nov 27, 2011
  6. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

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    He's in Maryland and driving to Virginia. In both of those states, like Maine, it's only illegal to coast in neutral on a downgrade.

    Of course, that means he was breaking the law.
     
    #6 ItsNotAboutTheMoney, Nov 27, 2011
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  7. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

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    Fixed your post.

    NICE-off-gliding is risky in the same way grille blocking is risky. But with grille blocking you can monitor temperatures.
     
    #7 ItsNotAboutTheMoney, Nov 27, 2011
  8. Tideland Prius

    Tideland Prius Moderator of the North
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    True but SHM in D will net you 2.5L/100km (94mpg) in that same section, won't it? I fuelled up this morning (temps are 10°C/50°F and the engine is warm) and went on the 50mph highway and on the SHM sections, I can achieve 94mpg but they will be negated by the pulse sections to 56mph. One way got me 69.2mpg and round trip end up at 65mpg. The terrain was not flat and there were hills to climb with that 50mph speed limit.
     
    #8 Tideland Prius, Nov 27, 2011
  9. Pinto Girl

    Pinto Girl New Member

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    Wow, overinflated tires and circumventing the HSD, all to try and eke a few extra miles per gallon from an already highly efficient automobile.

    It's also against the law, apparently, and might also aggravate other drivers, since it sounds like you're driving well below the speed limit.

    Not sure why it's work risking a blow-out or drivetrain damage, or why that last few miles per gallon are so important.
     
    #9 Pinto Girl, Nov 27, 2011
  10. bedrock8x

    bedrock8x Senior Member

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    Going down grade, > 4%, in neutral is dangerous and illegal in all states.
     
    #10 bedrock8x, Nov 27, 2011
  11. walter Lee

    walter Lee Hypermiling Padawan

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    Wowsers! :eek: I didn't realize that it was illegal. :(
    Well, I'm not going to be doing that again.:rolleyes:
     
    #11 walter Lee, Nov 27, 2011
  12. walter Lee

    walter Lee Hypermiling Padawan

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    When going downhill under PC, at superhighway speeds
    my 2010 Prius tends to accelerate faster than I can modulate
    and limit the the speed using PC and the HSI.:( For that
    reason, in past inter-state road trips I have been using
    cruise control instead of using the recommended hypermiling
    technique Driving With Load(DWL). :rolleyes: Going downhill, the
    electric motors' & ICE's ability to push the Prius forward
    becomes more effective and there's a sudden surge
    of power which I've found difficult to compensate
    for at speeds over 55 mph. When the Prius reaches
    speeds of over 60 mph, its fuel efficiency drops as
    wind resistance reduces the Prius' momentum.
    The other option is to allow the regen brake to slow
    down the Prius but they only recover about 30% of
    the energy - the rest of the energy is lost. Either
    way, my highway fuel efficiency drops when I use
    PC. :(
     
    #12 walter Lee, Nov 27, 2011
  13. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

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    In Florida the law against coasting on a downgrade was repealed.
     
    #13 ItsNotAboutTheMoney, Nov 27, 2011
  14. walter Lee

    walter Lee Hypermiling Padawan

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    FL = Section 316.2024 <== repealed ( April 27, 2011) :D
    My preliminary review suggest that MA and PA are NICE state :)

    But the list of not NICE states is pretty long... :(

    MD = MD section 21-1108
    VA = VA section 46.2-811
    ME = ME Title 29-A. Subch 1 section 2064
    CA = CA V C Section 21710
    RI = RI Ch 31 Section 22-6
    OR = OR Section 811.495
    NM = NM Ch 66 Section 7-360
    AZ = AZ Title 28 Section 895
    CT = CT Sec. 14-222. ( for commerical vehicles)
    MI = MI 257.678
    IL =
     
    #14 walter Lee, Nov 29, 2011
  15. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

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    Hmm. It almost seems you have it backwards.

    In hypermiling terms, if you're going too fast downhill you've made a mistake by having excessive speed at the crest of the hill. Once you've reached the crest there's nothing to do except try to let gravity accelerate you to as high a legal and safe speed as possible. You want to do that by holding a steady gas pedal or brake. 100% warp is perfect, but otherwise a consistent level of regen is better than having to brake harder near the bottom.
     
    #15 ItsNotAboutTheMoney, Nov 29, 2011
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