Using B for freeway exits

I can't imaging why you would want to do this. Regen braking and B mode both brake with the front wheels, so there is no gain there. The only difference is that you throw away some power using B, and you have to make the switch to B mode. If your freeway exit goes down a mountain for a couple of miles, then B mode is the way to go, otherwise, just step on the brake.

Tom

 

And if you forget to shift back into "D" you start eating into your fuel economy in a hurry.

 

I use "B" mode everyday on a short downhill through the canyon on the way home from work. The posted speed on the last two curves are marked as 25 MPH. The distance on the downhill is about a quarter-mile, so as soon as the road levels out, we switch back to "D". A couple of times we have forgotten to switch back and we quickly noticed the difference in the feel and sound of the acceleration.

We just use this mode with slight brake pedal pressure to prevent downhill speeds from getting to an unsafe speed for the 25 MPH curves. The transition to and from this mode is smooth and we have not had any problems yet. 67 K miles and counting.

good luck to you.

When I asked the dealer about this mode, he just said, "Don't use it". When I asked him why not he said again. just don't use it. Seems strange that they would add this feature if were not supposed to use it. One of my friends who bought and then sold his Prius said that in Colorado, the downhills were so long, that after the battery reached all green bars, there was no braking effect offered by the "B" mode. He sold it and went back to a VW Jetta TDI diesel.

I am wondering what Evan will say about this mode, and why he does or does not ever use it?

 

Unless you have an extended, steep downhill commute forget about the "B". Leave it in "D".

In this particular case the dealer knows what he's talkinb about. Just don't use "B".

 

OK, I might adapt to not using it, but does it actually hurt anything to use it?

Thanks in advance for anyone that can tell me. I might read the manual again and look for this info.

Thanks Evan for the link and the quick response. I will read this when I get home from work.

Dave

 

<div class='quotetop'>QUOTE(KD6HDX @ Aug 21 2007, 03:16 PM) [snapback]499863[/snapback]</div>

As Evan points out, it doesn't hurt anything other than your fuel economy, but it also doesn't help anything either. It's pointless to use it in this situation, so why do it?

Tom

 

From the linked article about "B" mode-

"But don't get into the habit of using "B"
to slow down unless you really need it -- that's sometimes hard to get used
to if you come from ingrained years of "gearing down" in conventional cars."

This was why I was using it and why I taught my wife to use it too when she drives that stretch of canyon road. I guess old habits are hard to break, but I feel better reading about it and knowing whats going on inside the motor.

I never used the "B" mode to save gas or charge the battery more.

Thanks again.

 

<div class='quotetop'>QUOTE(KD6HDX @ Aug 21 2007, 06:54 PM) [snapback]499985[/snapback]</div>

what about to get better traction in bad weather like standards do by shifting down?

 

I just used B for the first time for what it was meant for, slowing down a mountainside.

6% grade for 6 miles in Arizona mountains. Didn't really slow me down, even with the ICE howling at 4900 RPM and the AC blasting to drain the battery as fast as was filled.

Going down I-8 in California, 6% grade for 13 miles, didn't use B, just used the brake and modulated it, ICE engaged as it thought was necessary, everyhting was good.

B mode, why bother.

Wayne

 

<div class='quotetop'>QUOTE(FireEngineer @ Aug 22 2007, 12:42 AM) [snapback]500121[/snapback]</div>

I was starting to think the same during my trip to Hybridfest. In my earlier runs through the mountains on the trip I used "B." Then later in the trip I tried leaving the car in "D" and used moderate braking alone, presumably only enough to avoid mechanical braking until the battery was topped out. (It didn't take long; Can-View showed SoC increasing by 1% every few seconds during braking. Within just a couple of minutes of sustained braking the battery hit 80% or more, 82% at one point.) I think the steepest grade I saw (based on roadside signs) was 10%, and the brake was more than enough to slow it. The benefit, as Evan suggests, may simply be that "B" is easier on long downgrades. After the battery fills, it will be forced anyway.

 

<div class='quotetop'>QUOTE(SureValla @ Aug 21 2007, 07:54 PM) [snapback]500012[/snapback]</div>

With a manual transmission you get better traction by shifting up, not down. Down shifting increases the torque at the driving wheels, which increases the chances of wheel spin. With our snowy winters, we used to routinely shift into a high gear and lug up a hill to avoid wheel spin. The only place where I down shifted for traction was with my Jeep C-J5, which had a two speed transfer case. With that, you could shift into low-low and allow the wheels to slip at a controlled rate. There was no chance for spin because they couldn't turn fast enough to spin.

With the Prius, B mode is not a down shift, it just forces engine braking. It feels like a down shift, but it's not the same at all.

Tom

 

My rule on using B mode is that if I'm driving down a mountain and the battery is showing a full charge, I switch over. As soon as one bar dissapears I go back to D.

 

Bizarre I just thought B mode engaged the ICE engine without use of gas exactly the same when you downshift to engine-brake on a normal non automatic car, regarding the weight of the prius and the little size of the motor it may not be as efficient as we could imagine, but in case of full battery there is no more energy recycling so it's the only way without engaging the real brakes.

 

Well, that certainly is an education. I've tended to use it in certain situations, like when descending to the streets near my home, as both exits from the interstate have steep descents into stoplights, and were always hell on the brakes of my previous car. I've used it a bit on freeway exits, and other situations where I wanted to decelerate faster, or to balance the car in a corner the same way a heel and toe downshift to second did in my previous car. Perhaps using this is why I rarely see the seventh bar, and I should recalibrate what I do...