Do any of you drive in "B" mode? If so, when?

Discussion in 'Gen 2 Prius Main Forum' started by Southpaw1969, Jul 30, 2015.

  1. Southpaw1969

    Southpaw1969 New Member

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    Hi everybody, unfortunately I couldn't find any good information in the manual about shifting into "B" mode. Can you guys explain what it's for, what the benefits of using it are, etc.

    Thanks!
     
  2. wjtracy

    wjtracy Senior Member

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    Engine breaking...if you go down a big hill and you charge up the battery to FULL, if you listen closely there is a change in sound which is the regen braking system going off (you simply have no further storage to put the energy) and the bad news is you are now using your real brake shoes to slow the car. So engine braking helps. Many of us never need to replace brake shoes anyways so I suppose it would not be crime to actually use the brakes.
     
  3. Southpaw1969

    Southpaw1969 New Member

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    Ok, right before the freeway on ramp I normally get onto near by my house there's about a mile, mile and a half long decline where you can go about 60 miles an hour. Would it be OK to put on the "B" mode for that to just charge up the battery? At that time I know I can definitely coast that stretch of road at speed.
     
  4. DenToyPri05

    DenToyPri05 Junior Member

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    I use B to slow down. Whether I'm descending an off-ramp or preparing for the inevitable morning crawl on the freeway, I use B. You don't have to brake and then engage it by moving the "mouse" to the B position. You just mouse over to B. Ta-da! You'll feel the car slow, and you can watch the blue bars light up!
     
    #4 DenToyPri05, Jul 30, 2015
    Last edited: Jul 30, 2015
  5. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Above 24 MPH, it is always lower MPG and lower charge to the battery to use B mode. B mode is just for long downhills where the battery would fill up anyway, B mode keeps the friction brakes cooler so they do not fail, by using the engine to waste heat. If you are at the top of a long downhill (Donner summit to Sacramento, as an example) putting the car in B mode is good for the brakes, which you never want to overheat.

    Below 24 and above 7 MPH there are chances for B mode to help MPG slightly, but with a great deal of distracting shifting for a minor improvement in MPG. No regen happens below 7 MPH.

    B under the D in the Drive gears? | PriusChat
     
    #5 JimboPalmer, Jul 30, 2015
    Last edited: Jul 30, 2015
  6. bisco

    bisco cookie crumbler

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    never, not once in eleven years.
     
  7. DenToyPri05

    DenToyPri05 Junior Member

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  8. bisco

    bisco cookie crumbler

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    nope, but i don't live in denver.:cool: we have some decent ski hills in northern new england, but nothing like you guys. i can regen all the way down without ever friction braking.
     
  9. DenToyPri05

    DenToyPri05 Junior Member

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    ah, yes...the rocky mountain excursions make me either panic (2 purple bars), or feel smug (all blue bars, one bar shy of full, or the occasional intoxicating neon green).
     
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  10. fuzzy1

    fuzzy1 Senior Member

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    I use 'B' frequently for multi-thousand-foot descents. Yesterday, it was from Sunrise in Mt. Rainier National Park, at 6400 feet, down to the Park entrance at 2300 feet. Half that elevation loss is in a short distance.

    Above the threshold speed Jimbo mentioned, 'B' mode never has any battery charging advantage compared to regular regenerative braking. And a mile and a half of standard Interstate Highway, where the maximum allowed slope is 7%, is not long enough to have sufficient elevation change for 'B' to break even (by filling the battery) with normal regen.

    If your car will glide at only the speed limit while in D mode on your highway stretch in question, then 'B' is not necessary to prevent brake overheat. But if gravity would be causing the car to speed up to well above the speed limit or safety limit, then 'B' is certainly worthy of consideration.
     
    #10 fuzzy1, Jul 30, 2015
    Last edited: Jul 31, 2015
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  11. tanglefoot

    tanglefoot Whee!

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    I wouldn't use B mode unless you are negotiating long descents that result in the traction battery reaching maximum charge well before you reach the bottom. B-mode wastes energy away to help moderate the traction pack charge and reduce the need for the wheel brakes.

    I would not use B mode for highway off-ramps and short descents when there is still storage available in the traction pack. It won't hurt anything (aside from a tiny bit of engine wear), but it's not as energy efficient as riding the regen brakes (brake pedal), down the ramp, assuming the traction pack isn't already full.

    In winter driving, B-mode is nice for descending slippery hills by providing steady hold-back, making it easier to maintain control down the hill.
     
    #11 tanglefoot, Aug 2, 2015
    Last edited: Aug 3, 2015
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  12. R-P

    R-P Active Member

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    Just drove through Schwitzerland and used many B-roads last month. I used the "B" very frequently... A few minutes after reaching the summit, the battery is all green and I use it to not overheat the friction brakes*
    The rest of the year, I have no use for it (our highest hill is under 1000ft and snow is rare in the Netherlands)


    * I have overheated my brakes (Peugeot 405 break) in Italy once and loosing your friction brakes while going downhill due to (presumably) bubbles in the hydraulic braking system is not something I ever want to experience again... (The rear brake was probaby sticking and eventually, again presumably, evaptorated all grease from the rear ball bearing leaving us stranded on an Italian highway a few days later. Many Italians don't speak English (or Dutch or French) so a lot of hands and feet were needed to eventually get it fixed.:ROFLMAO:
     
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