Is frequent use of engine braking harmful?

[CigarPundit]

I think the problem with DCTs is that you don’t want to induce excessive or prolonged clutch slipping. There is a creep mode for crawling along slowly, which is preferred over staying lightly on the gas. Coasting normally to a stop light and letting the DCT downshift and disengage on it’s own is fine. But I try to come to a complete stop, let the clutch disengage fully, and then creep mode if necessary rather than maintaining a slow roll on the brake for an extended time, which will induce prolonged clutch slip. Under 15 mph, you can also flip it into neutral and back into gear, which will allow you to coast a little faster than creep mode and will not require coming to a complete stop. I do this too.

That said, I don’t think it’s a big deal if traffic conditions dictate. I would just be aware of it and try to avoid it if possible.

[zohaibkhawaja]

Originally Posted by CigarPundit

I think the problem with DCTs is that you don't want to induce excessive or prolonged clutch slipping. There is a creep mode for crawling along slowly, which is preferred over staying lightly on the gas. Coasting normally to a stop light and letting the DCT downshift and disengage on it's own is fine. But I try to come to a complete stop, let the clutch disengage fully, and then creep mode if necessary rather than maintaining a slow roll on the brake for an extended time, which will induce prolonged clutch slip. That said, I don't think it's a big deal if traffic conditions dictate. I would just be aware of it and try to avoid it if possible.

Yup that's what I read about. It was the wear that the clutch slipping had on the DCT. Thank you. Does anyone else have any method they use to prevent this?

[CigarPundit]

Originally Posted by zohaibkhawaja

Yup that's what I read about. It was the wear that the clutch slipping had on the DCT. Thank you. If anyone else has methods they use to prevent this please let me know.

See my edit above about flipping it into neutral.

[SenorFunkyPants]

The clutch packs won't suffer from wear at low speed "creeping".
You can also use 2nd gear for slightly faster "creeping".
I've never heard (in the UK) of a single case of a DCT box needing replacement clutch packs.
I let the car car decelerate to a stop using engine braking whenever possible...its how the regenerative system works to charge the battery.

[CigarPundit]

Originally Posted by SenorFunkyPants

The clutch packs won't suffer from wear at low speed "creeping".
You can also use 2nd gear for slightly faster "creeping".
I've never heard (in the UK) of a single case of a DCT box needing replacement clutch packs.
I let the car car decelerate to a stop using engine braking whenever possible...its how the regenerative system works to charge the battery.

Huh? Regenerative system? The F80 has an alternator. It’s always charging the battery when the engine is running.

[CigarPundit]

I learned something new by reading this thread. As I'm sure is apparent from my last post, I found SenorFunkyPants' comment about the regenerative system so odd, but I saw CanAutM3's post above and then looked up the "efficient Dynamics System. Apparently, "The alternator is generally charging the battery only when the car is braking, coasting or decelerating. The Brake Energy Regeneration system continuously monitors the battery’s state of charge, and can, if necessary, charge the battery even when accelerating in order to prevent it from becoming discharged (when the battery is charged to less than 80% of its capacity)."

I didn't know this, but it makes sense to not have the alternator consuming power and fuel unnecessarily. However, it is not necessary to use engine braking to keep your battery charged, and there is no "regenerative system" in the F80 as that term is generally understood (an EV's motor converting to a generator for the drivetrain battery under electrical braking).

[SenorFunkyPants]

Originally Posted by CigarPundit

However, it is not necessary to use engine braking to keep your battery charged, and there is no "regenerative system" in the F80 as that term is generally understood (an EV's motor converting to a generator for the drivetrain battery under electrical braking).

Indeed, BMWs using the phrase "Brake Energy Regeneration" is pushing the meaning of the word regeneration a little.
The ED system does quite a bit of "engine braking" which I find useful in rolling up to traffic lights for instance, timed right you don't even need the brakes until the last second.
Nothing like the regen you get on a Tesla though...which really catches you out when you first drive one.

[superbrew]

The only thing I can think of is that you can get oil sucked past the valve stem guides due to the increased vacuum, but I highly doubt this is a problem on a modern engine with tighter tolerances. That is what I have heard in regard to engine braking on motorcycles.

[mkoesel]

Originally Posted by zohaibkhawaja

Hey guys. Sorry if this is common knowledge, but I was unable to find an answer through research or on the forum. I think I remember reading or hearing somewhere that it is bad to let off the gas and not apply the brake with the dct (eg. coasting to a stop). Is this true? Thanks in advance.

Two points here:

1) As I was reminded recently, generally speaking, it is not possible to come to a stop with the DCT without using the brake (or manually putting the transmission into neutral which you should not do as a matter of normal practice when slowing or stopping). If you simply let off the gas, letting friction (both intrinsic and extrinsic) slow the vehicle, you will not come to rest (short of a colliding with something, I mean). Instead, as you decelerate, the engine will remain connected to the wheels and eventually move the vehicle along indefinitely in first or second gear (depending on your Drivelogic setting) at idle speed.

Now, if you happen to arrive at an incline at this point, it is true that the engine will not have enough power to keep the vehicle moving and the currently engaged clutch will at some point begin to slip. And it is also true that this situation would be bad for the hardware so you should avoid it. I suspect that, if engine RPM got low enough long enough, the TCU would relent and open the clutch to avoid a stall. But you would still be causing wear before it finally resorted to that measure.

Anyway, edge cases aside, there is no harm in leaving the car in gear and lifting your foot from the accelerator at speed, allowing the engine to help slow the car. Just make sure that, if/when you arrive at a speed that brings the engine near idle RPM and/or it starts to bog down before then due to a steep hill, you engage the brake and bring the vehicle to a full stop to tell the transmission to open the clutch (and keep it open until you apply the accelerator).

2) I am also guilty of using the word "coasting" to describe the situation where the car is moving with no accelerator applied, yet the engine is still connected to the wheels. Strictly, I think this is inaccurate:

https://en.wikipedia.org/wiki/Gliding_(vehicle))

"This is differentiated from coasting, which is running the vehicle in idle mode by disengaging the engine from the wheels, either by disengaging the clutch or setting the transmission or gearbox to neutral position."

So, technically speaking, coasting would be when the engine isn't connected to the wheels. In that case there would never be any risk of the engine stalling, and furthermore you eventually will come to a complete stop. That said, the only way to do this with a DCT is to put the transmission in neutral since there is no way to release the clutch while the vehicle is in motion. And, as I mentioned above in a parenthetical, generally speaking you should not do this as a matter of standard practice, if for no other reason than it is less "safe" because you have no way to accelerate immediately should the need arise.

[zohaibkhawaja]

Originally Posted by mkoesel

Two points here:

...

In this case, when reaching a stop is it ok to let off the gas and "glide" until using the brakes to come to a complete stop or should one use the brakes immediately after letting of the gas to prevent wear?

[mkoesel]

Originally Posted by zohaibkhawaja

In this case, when reaching a stop is it ok to let off the gas and "glide" until using the brakes to come to a complete stop or should one use the brakes immediately after letting of the gas to prevent wear?

Like I say, above, there is no harm in allowing the car to move with the engine connected to the wheels and without giving it gas. Just be sure that, when you do want to finally come to a stop, you engage the brake because that is the only way to instruct the TCU to open the clutch.

(BTW, "gliding" is really a special case of coasting with the engine off. Engine braking is the correct term for the condition where the car is slowing but still moving due to inertia, you are not on the gas, and the engine is still connected to the wheels.)

[zohaibkhawaja]

Originally Posted by mkoesel

Like I say, above, there is no harm in allowing the car to move with the engine connected to the wheels and without giving it gas. Just be sure that, when you do want to finally come to a stop, you engage the brake because that is the only way to instruct the TCU to open the clutch.

(BTW, "gliding" is really special cast of coasting with the engine off. Engine braking is the correct term for the condition where you are not on the gas but the car is slowing but still moving due to inertia and the engine is still connected to the wheels.)

Ok thanks. And what about letting off the gas, using the brakes to slow down a little, and then letting go of the brake pedal until having to come to a complete stop? Would this put wear on the engine/transmission?

[MaynardZed]

Engine breaking is harmful to your lap times. You should not be doing this at your track days. If you are, you’re going to be slow. Use your brakes for braking at the track.

This could’ve been what the instructor was implying?

Canyon or street driving doesn’t matter. Not harmful to your vehicle.

[mkoesel]

Originally Posted by zohaibkhawaja

Ok thanks. And what about letting off the gas, using the brakes to slow down a little, and then letting go of the brake pedal until having to come to a complete stop? Would this put wear on the engine/transmission?

That should be fine, again, as long as you do eventually apply the brake firmly to open the clutch when you reach the point where you want the vehicle to come to rest.

[backagain]

Originally Posted by mkoesel

If you simply let off the gas, letting friction (both intrinsic and extrinsic) slow the vehicle, you will not come to rest (short of a colliding with something, I mean). Instead, as you decelerate, the engine will remain connected to the wheels and eventually move the vehicle along indefinitely in first or second gear (depending on your Drivelogic setting) at idle speed.

My commute route is an express way with a speed limit of 50 MPH. Sometimes when coming to a stop light, engine braking slows the car down too much and takes a long time to get to the light. (The bay area drivers are not the most patient ones, me included.) So I would flip the DCT to neutral instead of tapping on the gas, for the sake of the blood pressure of the drivers behind me. (But I do always have my hand on the knob just in case I need to flip it into drive at any moment.)

[Humdizzle]

interesting about the clutch slip stuff with the dct.

if i'm stationary for a long time in my 458 (1st and on the brakes) the car will beep and put itself into neutral. i'm guessing this is to prevent wear?

regardless I don't think popping downshifts coming to a stop has ever caused a premature failure on an engine. I would still avoid dropping into first anytime the car is moving because of the stress on the drivetrain.

[CigarPundit]

Originally Posted by Humdizzle

interesting about the clutch slip stuff with the dct.

if i'm stationary for a long time in my 458 (1st and on the brakes) the car will beep and put itself into neutral. i'm guessing this is to prevent wear?

regardless I don't think popping downshifts coming to a stop has ever caused a premature failure on an engine. I would still avoid dropping into first anytime the car is moving because of the stress on the drivetrain.

I’d say you’re right in general, but I drop it into first literally every day as I’m rolling to a stop. Sure the DCT would do it for me, but I just enjoy it. If you are going slow, the car rev matches and if you do it right it’s actually perfectly smooth, which is kinda satisfying. You don’t need to get on the brake until the very last second to come to a complete stop.

[CanAutM3]

Originally Posted by Railgun

Tell that to the F1 guys.

They don’t need to be told, as they do not use engine braking to slow the car down. The brakes remain the primary source of deceleration with regenerative braking being the second one.

[CanAutM3]

Originally Posted by CigarPundit

I learned something new by reading this thread. As I'm sure is apparent from my last post, I found SenorFunkyPants' comment about the regenerative system so odd, but I saw CanAutM3's post above and then looked up the "efficient Dynamics System. Apparently, "The alternator is generally charging the battery only when the car is braking, coasting or decelerating. The Brake Energy Regeneration system continuously monitors the battery’s state of charge, and can, if necessary, charge the battery even when accelerating in order to prevent it from becoming discharged (when the battery is charged to less than 80% of its capacity)."

I didn't know this, but it makes sense to not have the alternator consuming power and fuel unnecessarily. However, it is not necessary to use engine braking to keep your battery charged, and there is no "regenerative system" in the F80 as that term is generally understood (an EV's motor converting to a generator for the drivetrain battery under electrical braking).

Just to be clear, when I mentioned “engine braking”, I was refering to the vehicle operating condition where the engine is connected to the drive wheels with no load applied while the vehicle is in motion. It is the only operating condition where the battery can be “efficiently” charged without using fuel, recuperating the energy from the vehicle momentum instead. By definition, this is regenerative braking.

Any other operating condition requires fuel to charge the battery. But as specified in the BMW documentation, those other operating conditions can be used to recharge the battery when needed if the battery charge becomes too low.

[FreeDarko]

Originally Posted by Humdizzle

interesting about the clutch slip stuff with the dct.

if i'm stationary for a long time in my 458 (1st and on the brakes) the car will beep and put itself into neutral. i'm guessing this is to prevent wear?

regardless I don't think popping downshifts coming to a stop has ever caused a premature failure on an engine. I would still avoid dropping into first anytime the car is moving because of the stress on the drivetrain.

Are you stating that it's better to come to a stop in 2nd gear with DCT than downshifting to first due to stress on the tranny?

[tropicalypso]

I wish I could convince my neighbor to stop engine braking his 340i past my house. He's very proud of the gun pops and cracks that his exhaust + tune makes.

[damageprone]

A set of new brake rotors and pads is cheaper than a new drive train. Just use the brakes.