Just trying to clarify - when shifting from D to B, or B to D, are there any restrictions? I.e. accelerator or brake must or must not be depressed? I know this should be straightforward, but the explanation the dealer gave me didn't sound right, and I can't quite seem to find it spelled out online or in the manual. Also, I've read that B-mode can negatively impact traction because it only affects the front wheels. Does this apply only to wet conditions, or to dry, curvy roads too? Wondering if I have to be concerned, for example, on dry, but twisty, mountain roads? As well as on long freeway descents in heavy rain. Wondering how one decides the safety balance between overheating the brakes vs. traction in these situations. Thanks!
As all regenerative braking is also front wheels only, it is likely all your braking is front only. Friction braking dissipates 80% with front wheels so even in the best of times the fronts do almost all the work. No car works the back brakes very hard. Until someone reports overheating the friction brakes, there is no safety issues with braking. And no, you do not need to be concerned, all Prius have Electronic Brake-force Distribution to prevent any wheel slipping. (and I am not sure where you would need B near San Diego, Mt Palomar?)
I rarely used B mode, but when I drive to Ashville, NC I will engage it once or twice, especially driving home when I'm coming down the hills. The rules of thumb I use; I need to control my speed and my battery is fully charged. You can engage B mode any time, but I would use caution if the roads are wet or slick. You don't want to disrupt the traction you already have. It's best to anticipate when you'll need to use B mode and engage it before your speed gets away from you.
It is. You just shift whenever you want. The system decides how to actually control the engine. You're just telling it that you'd like to use the engine for some slowing. What in the world did the dealer tell you?
You can shift between D and B all day long, any pedal input. The only thing that will wear is the shifter.
Thanks all! Yeah, close guess with Mt. Palomar - the trip back down from Julian had me on the brakes enough to think I should figure out B-mode for next time. I often "feel like" I should use B mode if I'm in a situation where on my previous automatics I would have downshifted into second or turned overdrive off. Though I would have done those things even on steep urban descents in the previous cars to help keep speed under control and save brakes. It sounds like in the Prius I should really save B mode for the mountains? As to what the dealer told me that sounded odd: it was regarding shifting back from B to D. As I recall, he said that you should shift from B to Neutral, and then Neutral to D (which sounded rather awkward if you had reached the bottom of a long grade and needed to accelerate immediately.) Maybe he just meant that's how the shifter works - but he said this only applied B to D, not D to B. One of these days I'll just take the car to an empty lot and just try it out, but wanted to make sure I at least knew any rules about the pedals. Thanks!
Your dealer wrong. B back to D is fine. You are correct, shift to B when you would shift to L, someone at Toyota was too honest to call it L when it does not use lower gears. (I walked the PCT east of San Diego, and was thinking of what was tall. We had a food drops in Julian and Mount Laguna.)
Drove it around an empty lot today to try out the D -> B -> D switch. I think I understand what the dealer was trying to say now. The switch from D to B is pretty much directly back into B because of where the shifter is sitting. But when you go back into D, you do need to move the shifter to the left first and then back. The way he explained it sounded to me like you were supposed to deliberately shift into Neutral at some point. Maybe I'd have been less confused if he just said, "Try it out, you'll see how it works." But props to him for trying to explain the shift lever in detail.
Just shift it. There's no need to do anything special. Just go from one to the other, quick & direct.
Yeah, that's probably how I'd explain it if I were a dealer. ;-) Still, in my parking lot tests, I think I managed to not get back into D once because I didn't flip to the left first... so it's good to realize it's a slightly different movement in one direction than the other.
Sounds like you have not done much driving in real mountains.......or have forgotten how hot the brakes can get when using them alone. Just because nobody has "reported" it doesn't mean that it won't happen. And what the B does is apply engine compression braking which the electronic braking controls would have no control over......unless maybe you also had the brake pedal mashed pretty hard at the same time. And as for the original question: Moving that lever to B really doesn't engage anything mechanically but sends a signal to the control computer(s) to apply engine braking. If the Toyota engineers did it right, the computer program will keep it from engaging in such a manner as to tear up the engine or motors or transmission. And yes, applying it at an inopportune time can cause a loss of traction on the front wheels.
I'm assuming an inopportune time would be if you did the shift itself while in wet slippery conditions? Is it just the shift itself that could cause the loss of traction, or actually driving in B mode? I.e., is there any problem driving with B mode on your garden variety twisty mountain road if you do the shift with car going straight and well under control? Should B mode not be used at all if the roads are wet? thanks!
A lot of it depends on the condition of the road surface such as grooved concrete versus asphalt. You need to get the car up to speed and put it in "B" to see how it feels and what to expect. That should allow you to determine whether it's something you'd want to do when you encounter wet pavement.
Or perhaps the difference is that I shift to B at the top of the descent, not when I have already heated up the brakes. I am not sure that qualifies as a real mountain, but it is where I play with B This is more a real mountain,with those speeds on an Interstate, but I drove it in my previous Toyota, not my Prius.
Two ways to get into trouble. 1=wet or slippery 2=excessive speed.....on what you think is a road with good traction. What gets you in trouble with the brakes is using them HARD for LONG periods so that heat builds up. So first slow down with the brakes to a "reasonable" speed and then engage B and let off the brakes.......or engage B as you start down the hill. As with a lot of other things, no need to have OCD about this, just use common sense.
Great, all sounds like what I would have expected then. Tried B out on an actual hill tonight, and it behaved more or less like the "Overdrive Off" button in my old Corolla (or maybe a little more, like a downshift) so that's good. Only part that seems to not behave as I would have expected is that it's a somewhat different motion of the shifter to go into vs. out of B mode (fairly self-evident while looking at the shifter, but not so much while looking out the windshield) ... So I guess it's good that I was at least OCD enough to try out a few shifts in a parking lot first.
Over the years Prius Chat gets so many questions and different approaches to using "B" that I really think Toyota needs to elaborate how and when to use it. Not just this thread but numerous ones, it seems like a lot of Salesmen, and Toyota dealership people don't even know how it should be used and employed. For me personally, I just don't think of the Prius "dongle" as a shifter. I think of it more as a HSD input selector. If you just tweak your thinking, then the idea of shifting from "D" to "B" while driving isn't as nerve racking. Even though the visual set up is similar to a regular automatic transmission and we have long history of manual clutch, transmission "shifting"...the Prius knob isn't really a "shift" knob, it's much more an input selection knob. I ONLY use "B" on long descents down big hills. Which is relatively rare for me. I do use it when it happens, but that's the only time I employ "B".
I was thinking about something similar today. I'm used to wanting to hit "overdrive off" (my old Corolla's option) on relatively short but steep hills that I travel regularly - just to save wear and tear on the brakes. But I'm guessing this ends up being a trivial issue on a Prius, since overall the friction brakes are used so little.
