Electric car: does the "B" setting improve economy?

Reed_Richards

At present I have a hybrid car.  This has a "B" gear which, in my understanding, effectively gives me engine breaking, I only use it when going down a very steep hill.  I'm about to get an electric car and this has a "B" setting which supposedly gives you more regenerative breaking.  I can't figure this out, why would you want any breaking not to be regenerative and wear down your break pads unnecessarily?  As far as I know, my hybrid does all the regenerative braking it can manage,  If it's a no-brainer, why is it there as an option?  But reading online it seems to inhibit coasting (don't see why) and exactly how it works seems to vary according to manufacturer.  Is it a better option for fuel economy?           

Martyn1981

Hiya RR, it probably doesn't remove the highest regen potential, it's just that not all the regen will be on the accelerator pedal. I suspect max regen will still be there, but as you start to press the brake pedal, before you reach the point where the actual friction brakes are used.

The main advantage of having more regen on the accelerator pedal (as you lift off more) is the ability to drive in 'one pedal' mode. This will depend on the EV, since one with a small battery such as a PHEV, or like our 28kWh IONIQ BEV, may not be able to provide enough regen to avoid the brake pedal use in some circumstances. [Also not all BEV's (again like our IONIQ) will apply the brakes for you, to bring the car to a full stop - so around 4mph or so, when regen ends you'll need to use the brake pedal to stop and hold the car.]

Our IONIQ actually has 4 regen settings, 0, 1, 2 and 3. I use the highest all the time, to minimise use of the brake pedal, but max regen is still applied (regardless of setting) as you push down on the brake pedal, before the brake pads kick in.

From a safety point of view, I like the idea that in an emergency situation, or just when something sudden happens and you need to brake, then at the point your foot has left the accelerator pedal, you are already at max regen, before your foot has moved to the brake pedal and pressed down. May only be a fraction of time, but it can all help.

Keep_pedalling

I drive a VW ID3 and its B mode it does not allow me to adjust the level of regenerative braking (unlike some other makes) , and I keep it in D for most of the time. This does not mean RB is not used when you hit the breaks and under normal breaking it will still provide 100% of the breaking.

On country lanes B will slow me down too quickly if I take your foot off the go peddle, so for instance it stops me coasting down gentle hills. On A roads I tend to use adaptive cruise control most of the time which decides when RB is to be used. I do stick it in B on the odd occasion I have to drive in heavy town traffic though. 

If I had a car where the level of RB could be adjusted I would probably use the B mode more. 

Ayr_Rage

If it's a Toyota hybrid, then ONLY use B going down steep hills for engine braking, it will not improve your economy or regeneration at all.

All-electric vehicles with a B mode will be different, as always, read the manual.

Netexporter

I nearly always have maximum regen set. Once you've got used to how much braking it will give you the mechanical brakes almost become redundant. In fact I have to remind myself to use the mechanical brakes occasionally, just to keep the discs shiny for the MOT. I live on the edge of the Cambrian Mountains and haven't found a hill that regen can't hold me at a safe speed on.

You do need to be aware that regen will be less effective when the battery is near full charge, although that is only likely to occur when setting off from a home charge. It is unlikely you'll have a full battery if you use public charging.

Martyn1981

Keep_pedalling said:

I drive a VW ID3 and its B mode it does not allow me to adjust the level of regenerative braking (unlike some other makes) , and I keep it in D for most of the time. This does not mean RB is not used when you hit the breaks and under normal breaking it will still provide 100% of the breaking.

On country lanes B will slow me down too quickly if I take your foot off the go peddle, so for instance it stops me coasting down gentle hills. On A roads I tend to use adaptive cruise control most of the time which decides when RB is to be used. I do stick it in B on the odd occasion I have to drive in heavy town traffic though. 

If I had a car where the level of RB could be adjusted I would probably use the B mode more. 

You've reminded me of a quick spin a friend took me on, when he got a BMW BEV. On a straight road with nothing ahead, he lifted full off the accelerator and it only applied a small amount of regen, but as we approached a very hard bend (same road), and he lifted full off, it applied high regen. I thought that was very impressive, the way it was using sat nav to moderate regen. I think he said he could set it for higher regen at all times, so a nice choice.

JKenH

Back to the OP, does it improve economy? It depends. 

Yes, it is better to use the B setting to slow the car down than just use the brakes. With the brakes all the kinetic energy is wasted as heat. With B mode it is used to recharge the battery, thus saving energy. However not all the energy is converted back to electricity and further losses occur then reusing that electricity to drive the car again. Perhaps 50% of the kinetic energy is lost.

No, it is more efficient (where possible) to allow the car to coast, using the kinetic energy to propel the car rather than recycling the kinetic energy through the battery. D mode is a half way house. 

So it all depends on driving style and where you are driving. If you are in a hurry B mode can actually be the better option. If approaching traffic lights that are green you can push on and if they change at the last minute B mode will recover more energy than D mode. If the lights stay green you have lost any energy. If you aren’t in a hurry it is far more efficient to anticipate lights or corners and decelerate slowly, avoiding any regen if possible. B mode I think makes it less easy to modulate the deceleration. 

The current Leaf has a brilliant display setting with white bars indicating whether you are using energy or blue regenerating it and the secret is to drive the car so neither white or blue are illuminated. This is particularly useful going downhill as without this you sometimes just can’t tell whether you are driving or regenerating. 

Ayr_Rage

@JKenH the OP has a hybrid, not a fully electric vehicle so using the Leaf as an example is not really valid.

I have had Toyota and Lexus hybrids and the B mode is not for general use.

JKenH

Ayr_Rage said:

@JKenH the OP has a hybrid, not a fully electric vehicle so using the Leaf as an example is not really valid.

I have had Toyota and Lexus hybrids and the B mode is not for general use.

I did see that but I was thinking he wanted advice about the BEV he was buying. 

“I'm about to get an electric car and this has a "B" setting which supposedly gives you more regenerative breaking.  I can't figure this out…” 

thevilla

Tesla Bjorn on YouTube did a test of b and d mode and concluded b was more efficient.  I reckon it depends on your preference and driving style and wouldn't be too hung up on it.  For the record, we use b mode in our Leaf although we also use e-pedal so not sure b gives any more than that.  Oh heck I've added another variable.

Reed_Richards

Yes, I did want advice on the BEV I am about to buy.  I was particularly confused by being used to a B gear on my hybrid Toyota.

I still don't see why an EV would ever want to apply the brakes unless regen alone was not stopping the car fast enough.