Downhill driving question

You are more familiar than we are about the road you are referring to and the circumstances of your drive.

If you can safely drive those hills without overheating your brakes, then feel free to do so. Just keep in mind that brake fires are nasty, and you usually won't know it's happening until things are getting out of control.

The B mode uses the engine to brake the vehicle on down hill runs so you can ease off the brakes and allow them to cool down.

 

I think that in this unique case, you would be better off using the "B" setting for two reasons.

First, chances are you are going to be on the brakes some of the time and therefore will get some regen. But more importantly, you will save a ton of wear on the friction brakes over time, at the expense of a little regen gain.

Second, you will decrease the wear and tear on your gravel road using "B"
If you can descend the road at a stead speed, without having the brakes grab at the gravel, you will disturb less of it. Also It will save your tires a bit in my opinion.

In normal driving, I have found that once the bars are fully green the HV battery is 75%. Further charging is available up to 80%. After that point, you are better off saving your brakes and using "B".

Icarus

 

Don't have my Prius yet, but from what I've read, you should use B below 7 mph to minimize wear on the brake pads (no regen below 7 mph, so it is all friction braking).

Above that speed, you can use B, but your regen would be greater with the brakes. However, if you have 7 or 8 bars SoC at the bottom of the descent using B mode throughout, then there is no reason to use the brakes except as required with B to keep speed safe. Once the batteries are charged (8 bars = 80% max allowed), there is no further benefit to regenerative braking, the car will use friction brakes, and you should use B just as a normal tranny would use L or 1 (to stay off the brake pads).

By the way, my STATE doesn't have 500 ft elevation change (not quite accurate, but it sounds good)

Corrections, anyone?

 

BS!

In the real world, the engine and transmission don't really care.

In a clutch car, down shifting to slow down, the wear is on the clutch. You can over come that wear somewhat by double clutching, keeping the rpm up for the lower gear as you let out on the clutch, and THEN get off the gas and let the engine slow you down.

Use the "B" and it will be fine, IMHO.

Icarus

 

Not to pick nit with you Evan, as you are really the expert, but,,

I agree that stopping from 8 mpg to 0 is little wear and tear, but a long down grade @ 5 mph, day after day WILL have significant wear on the pads and rotors. (Not that many of us do that routinely).

Icarus

 

Not to put too sharp a point on this, but Evan is correct. Whether to use B mode or not all comes down to whether the HV battery is reaching maximum charge. Just look at the battery display when you go down the hill (not in B mode) and see if you get green bars all the way up. If you do, then you should use B mode for at least part of the descent. If you don't, then B mode serves no purpose other than to waste energy.

As for bumpy roads, B mode and regen braking both work only through the front tires. In either case, friction braking will be invoked if the front tires loose traction.

Evan is also correct that friction braking takes over at around 8 mph. This is true whether you are using B mode or not.

Tom

 

This all depends on how fast you're able to go down this hill.
Remember, if you start with the engine off you can stay in "B"
at less than 20 MPH without the engine coming on, and that
automagically gives you a little more regen between about 11
or 12 MPH and up to 19 MPH. That lets you be a little less
likely to have a bump kick the regen out, too. So there's your
first level of "holdback" if that's the right speed range.
.
Otherwise you're on the brake pedal, carefully and lightly to
try and collect as much regen as possible. If you start with
a low SOC at the top, you should be just getting into green
after 500 feet of drop. The full allowable range of the pack
is good for about 600 [read the calculations here]. So if you
manage to get the engine shut down before the descent [look into
an EV button if you haven't] you'll be able to get down and
then a respectable distance away from the hill without
burning a drop of gas.
.
Let us know how the practice sessions go; sounds like you've
got a nice little test environment there as part of your daily.
.
_H*

 

From what I've read, these cars don't toast their brakes very quickly, and a brake job isn't a huge expense. Likewise, I'm assuming that Toyota knew what they were trying to accomplish when they put in the "B" feature. If it were me, I'd use both, sometimes one, other times the other. I doubt that you're going to do any major injury to your Prius either way. If you need new brakes at 80-100K miles, big whoop.

 

"B" is a feature of the Prius designed for safety and to lessen the strain of a relatively steep downhill drop. Why not use it as intended? Further, from a human standpoint, if their were no difference between the two, or even if there was a slight difference in favor of "D" gear, wouldn't the thought of making your husband happy be worth something?

 

Why use it if it does no good and hurts mileage? The Prius gives you the instrumentation to determine whether it's needed or not. If it were a one-time trip down an unknown steep hill, then by all means kick it into B mode, but on a route you drive all the time, use your head and figure out whether it makes sense. As hobbit points out, if your SOC is low, put all of that energy back into the battery. If you hit the top of the hill with a medium to high SOC, then stick it in B. It's not that hard to understand.

Tom

 

When you have a full green battery on the MFD that is the green light to use B.

Using brakes lightly on a slope if there is room in the battery for more electron doesn't use friction brakes only regen so brake away. ABS works on the brakes too so it is safer from a cotrol point of view.

Try stopping at the bottom of the hill and feel the front wheel near the centre, if it isn't hot you haven't used much brake, mostly regen.

I use B at the bottom of an 80km/h (50mph) 2 kilometre 11% grade but only if my battery is all full green.

 

Brake or B?

Hi cyberprius, welcome to PriusChat! I have a similar situation, but my road is paved and I live at the bottom. I usually just use the brakes and regen, and my battery is usually green and frequently full at the bottom, but that won't hurt anything. Since you're driving further, that full charge will help you save gas.

One thing you may notice, and it startled me the first time, is that your ICE may cycle on and off when you come to a stop at the bottom with a full green battery. That's the car wasting electrical charge to protect the battery from being overcharged. I couldn't figure out why the ICE was running with the battery charged. In fact, it was the motors spinning the ICE to lose charge.

If you're in the Portland area, check out the local HSD club in my signature.

 

I agree with Bill Merchant:
I live on the side of a mountain... it's about 1.5 miles down to the major street... I have been using the brakes down the mountain for almost 3 years, no wear as everyone has mentioned, above 7 mph...
Control on various turns needs normal foot brake control, not the b option, use that for the 10 mile interstate coming down the mountain..