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Discussion Starter · #1 · (Edited)
I would appreciate POV from owners of T8 hybrids as to when and why you use the "B" vs "D" gear.

I drove two different Lexus Hybrid SUVs for nearly 11 years and am comfortable how the Lexus RX hybrid implementation works, as well as what I could and could not do to improve my performance vs MPG and vice-versa. Last week I placed a new 2020 XC60 T8 Hybrid on order. I have read the XC60 T8 owner's manual front-to-back and scoured the web, but it's still not crystal clear to me what's really going on with some of Volvo's hybrid implementation, so I'd appreciate clarification and practical advice from others that drive any Volvo T8 -- which I suspect are all similar from model-to-model to what I'll have in my XC60, except of course the varying performance given physical vehicle differences.

What I know:
  • Lexus hybrids do hybrid traction battery regeneration automatically during most of the braking process.
  • Lexus hybrids also automatically regen as the ICE brakes against itself with driving -- not requiring any further owner action, e.g. going downhill or as you take your foot off the brake when the ICE helps slow you down. This works really well, as e.g. when I drove my old RX450h's from SoCal to Vegas which is 300 miles one-way on mostly freeway -- and 2K feet higher on a very long and mostly gradual incline from where I live near the coast -- with similar traffic and speed, for each of those trips I consistently got 3-4 less MPG on the way "uphill" to Vegas, than on my way "downhill" home when my MPG soared in comparison.

What I'm puzzled with:
  • From only reading the XC60 T8 manual, I'm left with the impression that unlike what I know with my former Lexus RXh's, the Volvo T8 Hybrid implementation only performs the automatic braking version of regeneration when you are in "D" gear. If you also want the Volvo T8 Hybrid to perform regeneration when the ICE is braking against itself in normal driving, you have to run in "B" gear.
    • Of great interest to me is neither of my former Lexus hybrids had a "B" gear to select from, yet did auto regeneration on downhill and "foot-off-the-brake, slow to a stop" without any driver interaction around town or at highway speeds.
    • So, why has Volvo made the choice to separate the two forms of regeneration and create a unique "B" gear? Is it perhaps that Toyota/Lexus prioritizes a little more MPG over performance -- or maybe try to make it more dummy-proof for the avg driver, whereas Volvo has chosen to place performance over MPG and give more of a choice? My Lexus RXh also had electric motors front & back with an ICE, whereas Volvo's Mild Hybrid has a single electric in the rear with the ICE. IDK. I must be missing some Volvo T8 basics here somewhere.
  • When I posed this to my Volvo salesperson (who was fabulous, but definitely has not lived with Hybrids and EV as I consistently have for nearly 15 years), she demonstrated PURE mode (which is like an EV with a really small battery -- I get it), and a dash touchscreen Hold/Charge function to force the T8 to recharge it's hybrid battery by keeping the ICE always on, but neither of those functions answered my question. So, I said to her, "Why wouldn't I just want to run in "B" gear all the time?" Her response was "You could." But she couldn't tell me "why" and explain the real differences between "D" & "B" gear -- and neither does the XC60 T8 Owner's Manual or some other official Volvo source I have been able to find -- hence I turn to the enthusiast community!
  • After placing my SC60 T8 order and several more hours research this past weekend, I found that more recent MY of Prius now have a "B" gear (they originally didn't). Unlike the T8, the Prius of course is a CVT like both of my old RXh's were, but I'm not seeing how that makes any difference. Anyway...

    Observing a YouTube video I eventually found, it seems on the newer Prius when you shift into "B" gear, the ICE comes on and remains on to both charge the hybrid traction battery (like Volvo’s T8 Hold/Charge function) as well as still using the ICE & transmission to slow the vehicle as you let up on the throttle or go downhill. When you stop, the Prius ICE goes off as I'd expect, but from that one example (and I may be over-analyzing), appears to then come on more rapidly at slow speed after you put your foot on the throttle than if you had remained in "D" gear — and the newer Prius ICE also seemed to then stay on until you stopped once more — meaning, MPG would suffer because you are not running off only the traction battery as long as you likely would have been in "D".
    • So, if a Prius "B" gear is like what Volvo is doing in a T8 (and for simplicity sake in this example, assuming I stay in T8 Hybrid mode all the time), I suspsect I should generally drive in "D" gear on my new T8 to maximize MPG with performance. The notable exception is if I were to get onto a longer downhill stretch where the XC60 T8 speeds up to the point I am having to use the brakes to slow-down, I should override the built-in Volvo hybrid logic and shift to "B" gear until the highway flattens out again — no different than how any of us have downshifted any 'ol ICE for years.
    • Does that make sense? I still don't know why the new Prius and Volvo have a "B" gear whereas Lexus has not for all these years -- unless again, it's something to do with being focused on performance or maybe giving more driving choice to enthusiasts? :confused:

Thanks to all for your help with my understanding while I wait for a ship date on my new XC60 T8.
 

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I've drove a Lexus n300h (mild hybrid) before switching to my current XC60 T8, so I understand your questions and confusion.

Here's my take at what you can expect when switching to your Volvo.

The D-mode behaves just as your Lexus. When releasing the gas pedal, the car brakes just as much as if you would drive a non-hybrid and felt the engine breaking. If you brake more heavy, even more energy gets delivered to the battery pack. On the driver's display you see 4 red/orange lines that indicate where the physical brakes start to help the braking process, but during regular driving and good planning you will only need the brakes when coming to a stand still.

If your Volvo has cruise control or ACC activated, the car will brake (with full regeneration if not too steep a downhill) and try to maintain set speed.

Switching to B-mode changes 2 things:

1. Regeneration braking is more pronounced, almost to a point where you can compare it to Tesla's one-pedal-driving. B-mode won't help if you plan your driving efficiently. I personally never use B-mode.

2. My Volvo mostly never wants to change gear from first to second if I accidentally activate B-mode. I'm not sure why it does that or when to use that feature.

Please ask more questions if I missed something!
 

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Discussion Starter · #3 ·
I've drove a Lexus n300h (mild hybrid) before switching to my current XC60 T8, so I understand your questions and confusion. Here's my take at what you can expect when switching to your Volvo...
I really appreciate your helpful reply. I assume that you have caught your XC60 T8 doing regeneration while in "D" gear, when you don't have your foot on the brake -- that would be great and along the lines what I'm used to.

It's interesting to me the Prius has introduced this "B" gear in more recent MYs, whereas it's not in the rest of the Toyota/Lexus line -- at least yet. Since Prius was their first hybrid implementation, which was then moved to the RX400h in 2006, perhaps we'll also see "B" gear show up as new MYs are introduced across their hybrid line as part of the whole Kaizen process they are so well known for. With Volvo being more of a youngster in the hybrid game, perhaps they were simply able to implement "B" in their first generation. We'll see. Time will tell.

Thanks again. Enjoy that T8!
 

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If I understand your explanation of Toyota's B-mode correctly, it has nothing to do with Volvo's B-mode. Instead, Volvo has a "charge" or "hold" button that will charge or hold the battery level.
 

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The difference between "D" and "B" modes is the vehicle begins regen when you lift your foot off of the accelerator pedal in "B" mode. In "D" mode, regen only happens when you press the brake pedal. "B" mode is a similar to "one pedal driving" but not nearly as aggressive as BEVs can achieve.

The manual is pretty clear on both of these topics. I only use "B" for better efficiency and convenience in (1) stop-n-go driving and (2) slowing down at long off ramps, approaching long red lights, steep hills, etc.
 

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"B" is basically the same as pressing on the brake pedal slightly, and so I only use it when doing that for a long duration is annoying (long steep downhill kinda thing).
 

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"B" is basically the same as pressing on the brake pedal slightly, and so I only use it when doing that for a long duration is annoying (long steep downhill kinda thing).
This.
In D, if you lift foot from brake, it still regenerates, just a little, judged by the dial needle is in the charging zone.
Regeneration is good but it is not wise to accelerate by using more power than necessary and regenerate immediately because you need to slow down. For this reason and also safety habit, I don't like the so-called "one pedal drive" on some EV.

B is same as D with mild braking force applied. It is useful for long downhill road so your foot doesn't feel stressful.
 

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I use B mode as other have stated above. Additionally, when I'm in congested fast moving traffic and I'm driving more aggressively I'm in Power and B with the battery on Hold. I like the on/off functionality as the car slows down just a little bit more as my foot moves over to the brake pedal.
 

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I live in a hilly area, and I mainly use B mode when going down a long hill, especially when there is liable to be a traffic light at the bottom. It's really great in that scenario. Also when traveling at some speed and a traffic light turns red ahead of me. In that case, I'm regenerating all the way up to the light. So handy and often no need to touch the brake pedal.
 

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Personally, the only time I find it useful is going downhill. It basically functions as a slightly lower gear and regens more aggressively.
 

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Discussion Starter · #11 ·
Thanks to all. I now have a much better grasp how the T8 “D” vs “B” works, and look forward to trying it out myself on my own XC60 T8 — hopefully sooner than later!
 

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2. My Volvo mostly never wants to change gear from first to second if I accidentally activate B-mode. I'm not sure why it does that or when to use that feature.
Unless your car is defective, this is nothing but operator error. I know because I felt the same way until I read some and learned what I was doing wrong. I used to tap the shifter down a few times without even looking at the driver display just to make sure it was in B mode. What actually happens is that once you're in B mode, tapping the shifter down again will go into manual shifting mode, which is somewhat useless since it only lets you DOWNshift. The only way to upshift is to tap up and go back to D mode.

Sent from my SM-G975U1 using Tapatalk
 

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My previous car was a MY 2006 Toyota Hybrid Highlander. It had a B mode. I gave that to my granddaughter and now drive a MY 2018 XC60 T8. I live in an area with long downhill stretches where I often use(d) B mode - on both vehicles. I can confirm all the folks who gave accurate answers here, which was most of them.

  • In D mode, you get minor regeneration when you take your foot off the gas pedal. On both vehicles this is true whether the ICE is running or not. With the Volvo T8, regeneration from the electric motors still occurs even if you have engaged the Hold function. (More on that below)
  • B mode on the Toyota, ICE running or ICE off, functions identically to B mode on the Volvo T8. B mode tells the computer to slow the car more by increasing the amount of regeneration.
  • B mode on the Volvo T8 does very little more than D mode if the battery is already full (or very nearly full). I can confirm that because I live at the top of a hill and notice not much happens if I try to use B mode for braking after my car is fully charged at home.
  • On the Volvo T8, downshifting again while already in B mode turns the ICE on and then uses the compression braking inherent in any ICE to further slow the car.
  • There is a freeway on-ramp at the bottom of one of the long hills I regularly drive. Depending on traffic, I have often forgotten to shift back into D mode when getting on the freeway. I only notice my error if there is a traffic slowdown or I get to my freeway exit a few miles later and notice that the car is slowing more than I expect when removing my foot from the gas pedal. Even with 5 miles of freeway driving on battery only in B mode, I haven't noticed a significant reduction in electric mileage when I've made this mistake.
  • The ICE will turn itself off while the Hold function is engaged in some situations. Think of what happens when you have used up the available power in the T8 traction battery. The battery never really goes to zero. There is always reserve power there to run the rear wheels for temporary AWD in slippery conditions or when driving at really slow speeds for short periods in city traffic. Additionally, on long trips with an "empty" battery, you will notice that the ICE turns off and you are running on battery for short periods. This is identical to what happens on Toyota hybrids, and most other hybrids as well. All that really happens with the Hold function is that you are telling the computer to regard the current traction battery status as if this set point was the "battery empty" percentage. The battery is allowed to go slightly below that point if needed, and of course, the battery will fill from regeneration when braking in traffic, going down long hills, or excess energy generated by the ICE. If the battery fills more than needed, the ICE will turn off and you will be driving on battery power until the Hold function set point is reached again. When driving in the mountains to a vacation destination, I often let the battery regenerate on the downhills, then turn the hold function off and on again to create a new higher set point. I've completely filled the traction battery this way so I have plenty of electric power for driving around town for the few days I'm at my destination. I think that is better for both gas mileage and emissions, but maybe I'm wrong.
 

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Discussion Starter · #14 ·
Appreciate the observations, advice, and comparisons. I’m anxiously awaiting a build date once the factory establishes one — for now, my expectation is I may not have my XC60 T8 until Jan-Feb, but there are always holiday miracles that may make it arrive earlier! :)
 

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The answers here are all correct, just in fragments. D mode does braking regen, and very very light coasting regen, more like a plain ICE automatic, you just coast with no real friction. B does the braking regen, plus coasting regen more aggressively, like driving an ICE with a 5-speed, you let off, you get more aggressive slow down. I enjoy driving both types of cars, so I appreciate B mode for doing more slow down when I let off the brake.. One Pedal Driving I guess they are calling it.
I also do this, I drive in D mode to work, which doesn't regen as much, because I can charge for free at work. I drive in B on the way home, to have more left, so I don't have to pay for as much charging time. :)
I, too, learned that if you keep pressing down past B, that you get shift-hold mode, as well as auto-turn-on of the ICE, regardless of if you need it or not. I've very watchful for that now when I try to figure out if I'm in D or B.
If you like to drive with more stretches of coasting, then D is the obvious answer as it's not going to slow you down. But I can discern a few ticks on the battery charge difference if I drive to work with D versus B, the regen is noticeable. The only negative, if you had to find one, is that in B, you are slowing down w/o a brake light on, but it's the same in a 5-speed ICE as well. Some people have told me they think that could be dangerous to the people behind you, slowing down w/o a brake light. PTUI, following too closely I call it. But I get it, I still use it tho.. free braking if you ask me.
And thank you for explaining that in the regen zone, that the red ticks means it's engaging brake pads, versus just generator. So what does "Off" mean past the red?
Cheers.
 

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The answers here are all correct, just in fragments. D mode does braking regen, and very very light coasting regen, more like a plain ICE automatic, you just coast with no real friction. B does the braking regen, plus coasting regen more aggressively, like driving an ICE with a 5-speed, you let off, you get more aggressive slow down. I enjoy driving both types of cars, so I appreciate B mode for doing more slow down when I let off the brake.. One Pedal Driving I guess they are calling it.
I also do this, I drive in D mode to work, which doesn't regen as much, because I can charge for free at work. I drive in B on the way home, to have more left, so I don't have to pay for as much charging time. :)
I, too, learned that if you keep pressing down past B, that you get shift-hold mode, as well as auto-turn-on of the ICE, regardless of if you need it or not. I've very watchful for that now when I try to figure out if I'm in D or B.
If you like to drive with more stretches of coasting, then D is the obvious answer as it's not going to slow you down. But I can discern a few ticks on the battery charge difference if I drive to work with D versus B, the regen is noticeable. The only negative, if you had to find one, is that in B, you are slowing down w/o a brake light on, but it's the same in a 5-speed ICE as well. Some people have told me they think that could be dangerous to the people behind you, slowing down w/o a brake light. PTUI, following too closely I call it. But I get it, I still use it tho.. free braking if you ask me.
And thank you for explaining that in the regen zone, that the red ticks means it's engaging brake pads, versus just generator. So what does "Off" mean past the red?
Cheers.
"Off" means your car is not turned on. Wheels are not powered unless you turn it on.
 

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And thank you for explaining that in the regen zone, that the red ticks means it's engaging brake pads, versus just generator.
It depends on the drive mode. In POWER mode (or INDIVIDUAL w/ DYNAMIC braking), the hydraulic brakes begin engaging at the same time as regen. That's what provides the "linear" braking feel.

Some folks ignore this scenario and keep posting inaccurate info.
 

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I just use B to slow down, and otherwise don't give it a second thought.
 
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