B Mode long trip driving in T8 lowers MPG?

WunderWagen · Nov 2, 2022

Hi everyone, did a search on this but did not see my specific situation mentioned. Recently did my first long distance drive in my 2022.5 T8 ER to my parents in Nevada coming from the SF Bay area. This was on Hwy 88 over the Sierra Nevada Mountains so thought it would be good to use B mode to take advantage of the hilly descents. However, it seemed to use more gas on my trip there than my previous 2018 T6 did. I was in Hybrid mode with the Battery Hold activated since this was a freeway 280 mile trip but it used up almost the whole tank of gas. My previous T6 would have a quarter tank left when I got there.

I also noticed that when on the freeway going from D to B it seems to bog the vehicle down almost like the brakes were dragging... this is with a light throttle being applied at freeway speeds and no deceleration. It seems like B mode causes some sort of engagement even when the throttle is being used to propel the car.

For my return trip home I kept it in D mode with the same settings and made it home with over a quarter tank. Some of that is based on the downhill portion being longer for my return trip but it also seems like B mode causes the engine to use more gas.

Has anyone else experienced this?

jtriebe · Nov 2, 2022

I only use the "B" mode, when I intentionally want to slow down; otherwise I leave it in D mode. My thinking behind that is that normally I want minimal drag on the car, no matter the circumstances, and D provides that. If I were to use the B mode all the time, every time I lifted off the accelerator, I would be braking and I don't necessarily want to do that. So only when I intentionally want to stop, or slow (as when entering a curve or making a turn) do I use B and then I flick the lever back into the D mode.

And only 280 miles on a tank of gas or even 3/4 of a tank is pretty poor. I'm unsure what is causing that, but I would advise not using the "Hold" mode, but rather just leave it in Hybrid, and use the GPS system to optimize where the car uses electric and where it uses ICE.

I've made three long range multiple day trips (1500, 1500 and 1100 miles) where I wasn't able to recharge overnight, and got 24-25 mpg on those. I've now got 8,300 miles on the car, and my overall fuel economy, including the above noted trips is 38.5 mpg. And with the exception of a few miles enjoying Polestar, my driving is exclusively in the Hybrid mode, but I use the B mode judiciously as noted above.

rsfpc05 · Nov 2, 2022

Any decent mileage heading up a hill while in B? Winds? 280 on a tank does seem extremely low. However B is tough on highway because it kills the coasting which can be long enough to turn off the motor in hybrid. Longer highway runs for the wife has yielded 37mpg of late (little lighter foot on the gas)

WunderWagen · Nov 3, 2022

Understood on the poor mileage... this was all freeway which is why I used Hold (battery would just get used up in the first 35 miles anyways if in Hybrid) and this was mostly all uphill going over the Sierra's (sea level to 8500 elevation). But even on a flat highway at freeway speeds I feel a drag like effect when switching from D to B... Not sure why since I was on throttle and not decelerating or braking.

ChrisZX · Nov 3, 2022

I think B mode plus battery Hold is the mileage killing combo. My feeling/understanding is that B mode puts the aggressive battery regen control to the top of the gas pedal, so we can have one-pedal-ish driving. When you put the battery on hold and cruise down the highway, you gas pedal control both the gas motor and electric regen (1 is putting out power and 1 is sucking away power), so you are putting some of the gas power toward the battery. In Hold mode, the battery tries to hold not charge, so extra battery from B mode regen is used up so battery is maintaining level. Essentially, you are using B mode to suck power away from gas motor toward the battery, which in turn used it up so it maintains level ( gas to electric to mileage = more fuel than gas to mileage).

When in Hold, it's probably better to use D mode. Or it may be better to turn off hold when you are on a stretch of road that you know you can regen a bunch.

WunderWagen · Nov 3, 2022

I think you may be right... D mode worked much better on the return trip. I do not use the battery when doing freeway driving since it seems to use the battery up pretty quick anyways which is why I put it in Hold. I use electric for around town driving.

Was not aware the Sensus navigation helped optimize hybrid driving... thought that was a AAOS feature. But then again I rarely use the Volvo nav as I prefer the phone. I will have to try that out on my next trip.

Gjohnsen · Nov 3, 2022

Same experience. The car is using more fuel in B mode. maybe its a AAOS SW issue? I find coasting is more effective, and fuel efficient.

lamarguy · Nov 3, 2022

This has been discussed many, many times in the forum.

When possible, coasting in D mode is always more efficient than regen, which only recaptures ~60% of the kinetic energy after losses.

ChrisZX · Nov 3, 2022

WunderWagen said:
I think you may be right... D mode worked much better on the return trip. I do not use the battery when doing freeway driving since it seems to use the battery up pretty quick anyways which is why I put it in Hold. I use electric for around town driving.

Was not aware the Sensus navigation helped optimize hybrid driving... thought that was a AAOS feature. But then again I rarely use the Volvo nav as I prefer the phone. I will have to try that out on my next trip.

I don’t like using battery on freeway either. Luckily, we haven’t had much highway needs … yet. Your experience will definitely help me prepare future trips.
I wish we have the ability to program where and when battery can be used, but I’m sure that too much to ask. Lol

WunderWagen · Nov 3, 2022

Interesting Lamarguy... did a search on B mode but nothing came up. Guess my surprise was feeling the drag switching to B even with partial throttle in use... no braking or coasting.

Gjohnson I have a 2022.5 T8 with Sensus so doubt it is related to AAOS.

jtriebe · Nov 3, 2022

ChrisZX said:
I wish we have the ability to program where and when battery can be used, but I’m sure that too much to ask. Lol

Why not let the car's computer determine when and where it uses the ICE versus electric? That is what happens when you use the Sensus Nav GPS to plan the trip. I use it every time I take a trip that I know exceeds the electric range of the battery and it works very well. I'll usually only have a mile or less of electric range when I arrive at my destination.

rsfpc05 · Nov 4, 2022

On a short sample, I used the Sensus gps optimization and got around 32. My wife just puts Hold on, no Sensus and has pulled 36ish. It’s interesting but either way, I’ll take it both ways for a 400hp 3 row SUV

cktan03.chris · Jan 9, 2023

Oh yes B mode all the way will increase your consumption. I do like you - use B during descents and slow traffic, and switch to D during high speed cruise. D allows for better (energy free) coasting. My 2 cents.

efenili · Jan 9, 2023

I did not know using the cars GPS would "optimize" the battery use but I'm not sure that small optimization is worth not using Google Maps on Android Auto/Carplay. Its easy enough to put the battery on hold for freeway speeds and then quickly change back to hybrid/pure when getting off a freeway or when traffic starts.

I do think using B on the freeway/highways is the way to go. I've made the SF to Tahoe/NV drive many times in my 21' T8 and generally will average 31-32mpg just turning on "hold" when above 40mph for that drive which means I have more like a half tank left in either direction give or take. Getting only 280 to me means either something is broken with the car or with the reporting.....thats something like 15mpg assuming the 18.8 gallon tank. I don't actually think the electric battery does anything to help your MPG for drives like that so no reason to use it at all IMO....there just isn't nearly enough juice to help, it'll be gone 20-30 minutes into your 4hr drive.

I do use B on the decents from the peak when crossing the sierra nevadas though BUT I will tap it into D for the flatter sections to make sure it coasts as much as possible. It's actually a kind off fun way to drive tapping back and forth to see how long you can go without using any power at all

Even with dozens of these drives I still average 46mpg on my T8 using those methods and almost exclusively pure during daily driving.

Pioneer4x4 · Jan 10, 2023

Using D to coast farther isn't the most economical.
First, I assume that you put it in D, and then let the car coast downhill, picking up speed (to a higher speed than you were originally travelling) which will the let you roll farther on the level (or up the next hill), right?
If so you are wasting energy, and recapturing less than you could have.
You are using AIR as the restriction to speed, which is wasted. If you used regen (B,light brake,ACC...) to limit speed you get both some of that air friction loss in your battery instead, plus you can use that to go further than what the coasting itself would have been.
If you think of it at the extremes it will make more sense. (moderate slopes, probably a wash)

lamarguy · Jan 10, 2023

Pioneer4x4 said:
Using D to coast farther isn't the most economical.

Yes, it is. The transmission is disconnected and you're coasting (coasting > regen).

Not trying to argue, because "physics", but regen is at best ~60% efficient (after energy conversion losses) and coasting is 90+% efficient. And, please don't introduce a "wind" variable...unless you're driving over 100 mph.

efenili · Jan 10, 2023

Hmm, I will have to try other strategies too

I don't use D for the downhills, only flats. So my general method is B for all the downhills but then at the moment I think B is going to slow me down to the point where I would need to use throttle I move to D to maintain speed on a flat section before another downhill where I move it back to B. So the downhills are big enough that even B doesn't slow the car down enough, its still picking up speed in these sections enough to coast on flats assuming I switch to D.

The idea (for me) was to never use the throttle or brakes. I understand that in B with a little throttle is essentially D but thats more footwork that I have to do instead of just toggling back and forth.

All of the above assumes I don't NEED throttle for any sections and in the sections that I do I do keep it in B while giving it enough to get through whatever section that is.

Pioneer4x4 · Jan 11, 2023

lamarguy said:
Yes, it is. The transmission is disconnected and you're coasting (coasting > regen).

Not trying to argue, because "physics", but regen is at best ~60% efficient (after energy conversion losses) and coasting is 90+% efficient. And, please don't introduce a "wind" variable...unless you're driving over 100 mph.

Sure, regen is nowhere near 100%, I have no idea (well, an idea), 60% sounds reasonable. But coasting without it is 0%.

Seriously, coasting faster is using the air to limit your speed, not regen. Capture that free energy. Think in terms of extremes.
Which of these statements do you disagree with?
1 - If you went down a fairly steep hill in b at say 20mph, you would basically capture "all" of the potential energy of the height of the hill, and reach the bottom with more charge in the battery.
2 - if you just coasted, and let the car roll, YES, you are going faster, and will roll further once you are at the bottom and on the level.
3 - the amount of EV charge gained in scenario 1 will take you further than just coasting in scenario 2.
Personally, I know that all 3 are true, definitively so. Some long down hills I have literally gained miles of EV range.
I would love to see other peoples MPG results over very long drives without recharging.
My personal record under VERY IDEAL conditions is 40.0xMPG over 830 miles in one day. (15.5 hours, 54mph avg)
Pittsburgh area to Connecticut and back. Capturing all those downhills in PA got me enough EV for a couple traffic jams in the NYC area. That was a perfect alignment of weather, time of day, temperature, solo driving (nobody else riding with me would have tolerated the mundane pace), no rush, weekend, that I will never have again.

lamarguy · Jan 11, 2023

Pioneer4x4 said:
Sure, regen is nowhere near 100%, I have no idea (well, an idea), 60% sounds reasonable. But coasting without it is 0%.

Sorry, I'm not going to debate the physics of energy conversion from kinetic -> electricity and kinetic -> potential kinetic energy.

2022 NYC S60 Recharge · Jan 11, 2023

Pioneer4x4 said:
Sure, regen is nowhere near 100%, I have no idea (well, an idea), 60% sounds reasonable. But coasting without it is 0%.

Seriously, coasting faster is using the air to limit your speed, not regen. Capture that free energy. Think in terms of extremes.
Which of these statements do you disagree with?
1 - If you went down a fairly steep hill in b at say 20mph, you would basically capture "all" of the potential energy of the height of the hill, and reach the bottom with more charge in the battery.
2 - if you just coasted, and let the car roll, YES, you are going faster, and will roll further once you are at the bottom and on the level.
3 - the amount of EV charge gained in scenario 1 will take you further than just coasting in scenario 2.
Personally, I know that all 3 are true, definitively so. Some long down hills I have literally gained miles of EV range.
I would love to see other peoples MPG results over very long drives without recharging.
My personal record under VERY IDEAL conditions is 40.0xMPG over 830 miles in one day. (15.5 hours, 54mph avg)
Pittsburgh area to Connecticut and back. Capturing all those downhills in PA got me enough EV for a couple traffic jams in the NYC area. That was a perfect alignment of weather, time of day, temperature, solo driving (nobody else riding with me would have tolerated the mundane pace), no rush, weekend, that I will never have again.

this is helpful. 40 MPG benefited from the EV usage. But if you are not duplicating the trip it would be hard to compare.
Did you look at the individuals segments or did you drive continiously?

I think under normal and generally level highway driving, very little regen will happen in many cars. In my vehicle, taking the foot of the gas pedal at these speeds in B does not slow the car down much if at all. Some people suggest that it actually is generating at some level and if so that would be counter productive then pure coasting (at a relatively constant Level. I do usually drive in B and can how see ow switching to D in certain circumstances and certain portions of the trip could be net more beneficial. I will look more closely today at the regen and next time I have a longer trip, I am going to try to break up the trip into segments and check what i see.

B Mode long trip driving in T8 lowers MPG?

WunderWagen

jtriebe

rsfpc05

WunderWagen

ChrisZX

WunderWagen

Gjohnsen

lamarguy

ChrisZX

WunderWagen

jtriebe

rsfpc05

cktan03.chris

efenili

Pioneer4x4

lamarguy

efenili

Pioneer4x4

lamarguy

2022 NYC S60 Recharge

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