Using B for freeway exits

[dbj]

Hello all,

I could not find this particular nuance by 'googling' this site, so here goes:

Has anyone tried using the 'B gear' when exiting a freeway? It seems like this might be useful, sort of like downshifting a sports car to slow it down without using the brakes. It seems to me that it might be smoother than using the brakes. (Yes, I know that the brakes contribute to the overall operation of the car by providing regenerative power over and above what I would get in 'B'.)

Out here, we seem to have an abundance of very short straights leading to significantly tight curves as part of the freeway system exits. Posted speed limits go from 70 mph on the freeway to 25mph on the curve a few hundred feet later. My comfort zone lets me take the curve faster than that, but I'd like a less drastic slowdown to my perceived safe speed.

For that matter, how about 'B' for normal corners and curves as well?

I know I could just try it, but I'm still a bit intimidated by this very new car, and afraid of doing something to hurt it! Would these actions likely lead to premature wear, somehow?

I had a friend who loved to downshift his Lotus for any slowdowns or curves, and he explained to me once (with more than a little tongue in cheek wryness) that he did it because "... gears are so much easier and cheaper to replace than brakes ..."

Thanks for any experience you may have.

little greenie

[qbee42]

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

[efusco]

Agreed, no benefit at all. Get off the gas as early as is safe. The gently but firmly apply the brakes to get all the regen you can so that you gradually increase brake pedal pressure until you get to your stop....or better yet so that you don't have to stop at all and can maintain your momentum.

[richard schumacher]

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

[KD6HDX]

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?

[Godiva]

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".

[efusco]

<div class='quotetop'>QUOTE(KD6HDX @ Aug 21 2007, 01:52 PM) [snapback]499853[/snapback]</div>

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? [/b]

Hobbit has an Extensive Review of B-mode that goes into all kinds of gory detail about the negatives of B-mode.

While using B-mode as you describe definately will not hurt the car or cause any problem it's also a waste of gas b/c at any speed over 20mph it forces the ICE to continue to run until you shift out of B-mode again. This burns gas and reduces the amount of regen you can achive b/c some of the potential energy is lost through the engine braking.

For the short downhill you describe I would go into stealth at the crest of the hill and then use the brakes to regen all the way down keeping the speed below 41mph the whole way so I could get max regen and burn zero fuel.

[KD6HDX]

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

[efusco]

Oh, and I didn't say I 'never' use it. I use it occasionally at speeds below 20mph b/c when you coast at those speeds in B mode there is not any/as much battery drain as there is in D and the ICE won't spin up at that speed. I also would use it on a very long steep downhill/mountain if I knew the battery pack would get totally full before I reached the bottom and thus force the use of friction brakes. Even then the benefit is questionable, it's just easier than concentrating on braking for that long distance.

<div class='quotetop'>QUOTE(KD6HDX @ Aug 21 2007, 02:16 PM) [snapback]499863[/snapback]</div>

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 [/b]

Again, the only thing it "hurts" is your fuel economy.

[qbee42]

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

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
[/b]

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