D vs B for 0.75 mile 15% windy downgrade

Up front, doesn't B mode behave differently on the Prime? Not sure.

If it was a regular Prius, in my Gen 3 experience, I think that would be fine in D, would just get to fully charged, by no means lead to an overheating brakes case. I reserved B mode for coming down Mount Seymour, a local ski mountain. And again, the Prime likely has more capacity, uses B mode somewhat differently.

The simplest and most effective way to find out is to try it. The Toyota engineers make a car that's fairly bullet-proof in day-to-day driving scenarios; you're certainly not going to break the car with a modest downhill.

 

A 15% grade for 0.75 mile is less than 600 vertical feet. That shouldn't overheat the brakes even without regeneration.

In my Gen3 non-plugin, I'd start with D, then maybe switch to B as the battery is nearly topped off. Or maybe not.

But your Prime operates differently, it should be able to regenerate all the way down without friction brakes regardless of which 'gear' you select. If the engine spins needlessly, you just might need to switch it from HV to EV mode.

 

Any debate about D vs. B is at the margins. Coast downhill in B when it feels right. Don't use B if you need to step on the accelerator (you can, but it isn't the most efficient---always do whatever gets you safely through the spot at the moment.)

 

there's a thread on using B regularly in EV mode Driving in "B" Mode Regularly ... in your case, I'd suggest to try out both modes and see what works bet for you ... me personally, I use B on downhills over D as I use the brake pedal less, it also has more regen.

 

This is steeper than the stretch of Cadillac Mountain road, which, for its 1200 vertical feet, I could gain about 20% charge on the battery. So, for your stretch, if you're looking to use only regen braking, then you'll probably recharge a little over 10%.

 

It comes down to what you are comfortable with.
While in EV mode with the battery not at full, B 'gear' is the same as lightly applying the regen brakes in D.

 

Wny not just set the cruise and let the car control tbe speed?

Posted via the PriusChat mobile app.

 

IIRC, that works BUT the computer might engage the extra engine braking when you are not expecting it and it can be VERY abrupt and unsettling.

There really should be no debate here. For safety reasons, you should use B if you are on a grade steep enough that you keep gaining speed with just occasional light braking. What does or doesn't go into the battery is not important in that situation.

 

Personally, I wouldn't use cruise on a steep downhill, and for a short hill like this, I'd be inclined to just carry on as usual, in D, using the brake as usual.

 

That may not be a good fit for the sharp turns.

Is that a new mis-feature on the Prime? It certainly doesn't happen on my Gen3 liftback.

This hill is short enough that simply riding the service brake is safe even on a non-plugin Prius. The Prime, when not completely full at the top, may well be able to re-gen the whole thing, or nearly so.

 

This reminds me of a past thread: an ongoing debate, about how far to let the hood drop when latching it.

 

No, sorry, that was an ASSumption based on how my C works.

What does yours DO if you go down a STEEP grade with the cruise set from before you crested the hill ?
It doesn't take mine long to "realize" that it can't hold the speed and switch to engine braking (B mode).

I would expect that any plugin model with the HV battery not full might work quite differently........for a while.

 

In my experience with a gen 3 liftback regen won't hold the car on a 15% grade. Actual friction brakes are used (by me) from time to time.
Do keep in mind, in a car, it would be very unusual to "overheat" the brakes. Especially on such a short hill. You would have to try very hard to do so. Like the fool on the freeway near San Diego trying to claim he had a "runaway Prius" a few years ago.

 

I use "B" mode on downhills frequently, especially when there is a stop sign at the bottom. It saves the brakes and the charging rate seems a bit higher. I got in that habit while driving in the mountains.

 

Meh, I'd vote to use it for mountain descents only. Other than that, you need to slow: step on the brake. Easy, avoids constant wear-and-tear on the shifter, and charges more.

 

Mine simply can't do B mode and Cruise Control simultaneously. It has a lockout, only one at a time is allowed.

My Cruise Control does use regeneration first, then engine braking, to control downhill speeds, but the transition is not:

Instead, it is a gradual and even ramp-up as the crest slope changes and the car starts rolling up. 'Abrupt' happens only if I manually shift from D to B when already going too fast.

 

Small correction:
Engine braking IS "B mode".
Thus, you can not MANUALLY select both Cruise and B mode at the same time........but the system WILL do it for you automatically........as you indicated above.

 

Sigh. This is one of those things where a single label is often used to refer to two similar but not identical things. And doing so adds to the general confusion.

I stick to the nomenclature that 'B mode' is the mode selected by the 'B' position of the gear selector. It uses multiple tools in a certain fashion. One of those tools is engine braking.

The engine braking tool is also used in somewhat different fashions by 'D mode' and by 'Cruise Control'. Cruise uses engine braking in a more similar fashion as 'B mode', but not identically.

Therefore, I refuse to conflate 'B mode' and 'engine braking' as meaning the same thing.

 

It looks like your bag of "nits" is about full; maybe time to get a new one.