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going down a slippery hill

Discussion in 'Gen 2 Prius Fuel Economy' started by tjoe78, Dec 9, 2006.

  1. tjoe78

    tjoe78 New Member

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    Going down a 1/2 mile yest. road was really sloppy--the trac. control light kept flashing the whole way--really scared me--never had it stay on so long. Kept light pressure on the brakes. I was able to stop almost at the end where I have to turn. I have winter tires. Would it be better to shift to B?
     
  2. efusco

    efusco Moderator Emeritus
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    I see absolutely NO advantage to using B-mode in this situation. Also, can't see why the TRAC would kick in going down hill...it only works when accelerating and it senses tire spin.

    Do you think it might have been the VSC doing it's job to keep you on the road...a car without probably would've been in the ditch. Sounds like everything worked perfectly to me.
     
  3. qbee42

    qbee42 My other car is a boat

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    No advantage to B mode. As for VSC, did you get a chime along with the trac control light?

    Tom
     
  4. pinball

    pinball New Member

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    Hang on a sec - B is exactly what you need to deploy. There's much less chance of locking the tyres and skidding when using the ICE/motors to slow you down than brakes alone.
     
  5. DaveG

    DaveG Member

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    <div class='quotetop'>QUOTE(pinball @ Dec 9 2006, 10:47 AM) [snapback]359782[/snapback]</div>
    I'm not sure that's entirely accurate for the Prius - after all, when you're slowing, it's actually using the electric motor to slow you down as it regenerates power anyway so there wouldn't be much difference between the electric motor slowing the car as it regenerates, and the ICE slowing the car in B mode.

    Dave
     
  6. cairo94507

    cairo94507 Active Member

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    <div class='quotetop'>QUOTE(efusco @ Dec 9 2006, 08:08 AM) [snapback]359672[/snapback]</div>
    With respect I completely disagree. My traction light illuminates when ever I am coming to a stop and my front tires slip on a man hole cover in the street. I am not on the gas and I am lightly braking when that happens. So I believe the condition as described exists. I would think B mode would assist with this problem too.
     
  7. efusco

    efusco Moderator Emeritus
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    Despite the disagreement, I absolutely stand by my statement that B-mode is not indicated here. ABS is the part responsible for preventing skidding...it offers active control...b-mode blindly slows without regard to skidding/slipping.

    I may be mistaken about the trac coming on during slipping while moving forward, and it will flash on briefly when the VSC activates, but I don't think it should kick on repeatedly during a long slippery downhill...that sounds like VSC.
     
  8. hobbit

    hobbit Senior Member

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    While it's usually a disadvantage to use "B" other than when needing
    to blow off a little more downhill energy than the battery can suck
    up, in the case of slippery roads all bets about energy recovery are
    off and "B" actually helps keep a constant retardation going but
    not wheel lockup [which, of course, would immediately be compensated
    for by ABS but possibly not in a way the driver expects]. Near the
    end of the B-mode article is some discussion about potential uses
    of the "falls on its face" feeling when coming off the accelerator,
    and snow and the like are probably one of those situations where you
    want that. In a MT car you'd be gearing down, and possibly dropping
    an automatic into "L" for the same effect.
    .
    But use your best judgement, find situations where you've got the
    leisure to experiment, and PRACTICE to determine what works best.
    You aren't likely to get great, efficient regen on stuff like that
    so it should take a back seat to control.
    .
    _H*
     
  9. pinball

    pinball New Member

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    For many years I lived in the Italian mountains teaching skiing.
    The best mountain car I ever had was a VW Beetle.
    With the engine over the rear wheels it had great traction on steep icy roads both up and down.
    I only ever had to put chains on twice in 8 years.
    The trick was to keep it in 2nd - and sometimes 1st gear, using the engine to slow you down rather than brake and risk inducing a skid.
    Usually it was a bit of both....however - lock your wheels up on an icy downhill bend and you end up in the ditch - I know !
    Incidentally in the mountains (Italy) the car coming down the hill has the right of way - think about it :).

    Anyway, I just applied the same principles to Prius on the basis that anything that will reduce your momentum down an icy slope has to be a good idea - except when skiing ! :)
    You'll also find that lowering the pressure in your tyres will give you a little more traction - but it'll affect your mpg.
    Don't try getting into B half way down the slope either !!
    Its either from the top or not all
     
  10. efusco

    efusco Moderator Emeritus
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    <div class='quotetop'>QUOTE(pinball @ Dec 10 2006, 04:34 AM) [snapback]359984[/snapback]</div>
    A thing or two have changed in automotive technology since the old VW! ;)

    Namely, ABS and VSC. The risk of skidding, even with firm braking, is markedly reduced with these.

    I do, however, fully agree that if one is going to use B-mode (which I still see no point in b/c of the ABS) that it should not be used to slow down once one has gained momentum...start it at the top as a speed control measure down the slope or not at all.
     
  11. pinball

    pinball New Member

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    <div class='quotetop'>QUOTE(efusco @ Dec 10 2006, 01:09 PM) [snapback]359997[/snapback]</div>
    I guess we're down to this: Is B-mode + ABS + VSC safer on a steep icy slope than just ABS + VSC ?
    I say Yes........... but then I say tomhato 'n you say tomato :lol:
     
  12. tjoe78

    tjoe78 New Member

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    <div class='quotetop'>QUOTE(tjoe78 @ Dec 9 2006, 07:46 AM) [snapback]359668[/snapback]</div>

    The slip control light was on, no beeping--I was going less than 25--so is that traction or VSC? The ABS was not on--I know what the pulsating feels like--it was not doing that. Sounds like some think B would be good at the TOP of the hill, while others say no. My husband is always saying the Prius has no compression going down a hill--always picks up speed. In all my previous cars (AT Hondas), I'd shift down at the top of the hill, and that would slow me down. The B mode is EXTREMELY noisy, and I think that scares me more!!