I think for all bmws for the longest time i had/have them. It occasionally pulses the brakes a second or two seconds whenever necessary. Not drag on the brakes all day in the rain. Will wear some but probably negligible. When we step on the brakes to come to a stop sign/light, we normally have to step it for many many seconds (then when already stopped, it doesn't count/wear). This random pulse/clean might be a fraction of the brake pads usage and probably is almost negligible. Also they said lightly/closely, not a full-force brake pads clamp like what we have to do to come to a full stop.

 

If this is true then I wish there was a user option to disable the function. Suddenly and randomly applying brakes is dangerous and the rust is only a visual thing. Anyway, next time I have rust I will take a picture and post it here, because I have had that on my brake disks. But perhaps I am the only one...

 

My (admittedly unsubstantiated) belief is that under normal driving, the last few feet (or inches) of coming to a stop simply uses the pads.

That's what my Audi e-tron 50 did - I could hear it.

During normal driving, I would not expect an auxiliary function in the car to try to do what is adequately performed by airflow and centrifugal force to remove excess water from the disk between uses. Disk brakes have been around a long time without such fancy sub-systems.

Yup. The consequences of the car mistakenly overdoing the 'drying' would seem too adverse for the benefit. (Back to that thread again). I reckon that the biggest benefit of brake drying would be enabling the car's owner to tell other cars' owners about the feature.

 

I can't help but think that this brake drying thing is solving a problem that I've never really had...

 

I agree. Solving a non-issue and causing potential issues down the road. When would this be useful? (a) on the track...wait you usually have slicks and you don't track in the rain! (b) on normal roads? Tire traction is the biggest issue in the rain. If it makes a difference, it is less than a secound. I know that is a lot in a car going 100MPH.

Only case I can see this really helping is that the roads were really oily, even still my other cars don't have it and I don't think the BMW brakes any better than my other cars. Stopping distance is really just tires and weight. Good/bad brakes only come into play after repeated stops or brake failure. I hope it doesn't do it when I'm on the accelerator.

 

Fortunately the i4 doesn't have a rear wiper or reversing would be really dangerous

 

here... straight from bmw usa ha ha...

 

All new BMW, or only some? He is saying all, but that includes the smallest and cheapest also. Anyway, I stand corrected if true, but I think I need to test this somehow. Also, if it really does this then it wears the brake disks or pads prematurely. It is also strange that you can't feel it when driving on highway and it starts raining. The other thing is, what's the point when raining heavily and constantly...?

 

I noticed that sometimes (usually when I slam the brakes) the regen meter on the dashboard goes all way down and fades to black. It's either maximum regen, or maybe (my guess) a sign that non-regen braking is engaged.

First I've heard of this!!
Now I gotta go try it.

I see that bar go gray all the time, and have asked the question before. I do believe that it just means maximum regen braking is exceeded.

When the recuperation meter fades to gray I assume this means that mechanical brakes are starting to be used.

I don't usually use B mode but I tried it earlier on today at high and low speeds and, with my foot fully off the brakes, the meter was not quite maxed out, braking with the left pedal gave (if the assumption above is correct) a bit more recuperation before pressing harder made it fade to gray.

I normally use minimum recuperation in D mode. When lifting off, I see maybe a third of the meter filling. Left pedal braking brings in more recuperation and eventually the meter fades to gray when I press the brake harder. Even with the meter graying out, the live vehicle display claims that the battery is charging.

This seems a bit at odds with the manual when it claims B mode has then highest energy recovery.

 

When the area is grey the car is still using max recoup but is also using friction brakes so this is why the live vehicle still shows recharging.
The manual is badly written- the bit under General is correct I.e. you do get a high level of recoup when lifting off the accelerator. They fail to make it clear that you get exactly the same recoup when pressing the brake pedal!

 

My i3 is a 2019 - no synthetic noise - quite dangerious while no pedestians register the i3 approaching.
The brake squeal is only first drive in the morning - and normally in Winter when it is a slight rust layer on the rotors.

The i4 uses the brakes much more (or I use the brakes more than my wife) so very clean brakerotors on the i4m50. Also the Autohold also engages brakes.

 

In the i3 - the noise is brakes screaming.
Last Winter my wife actually called me telling me that the car had a big problem, but it was only the brakes cleaning for the first 10 meters.

 

I don't know the i3 but generally all EV must generate noise when driving slowly. That's the law. That noise is not generated by the brakes. Even my i4 has a high pitch noise when driving slowly, the tone is almost the same as our Leaf had, and is also similar to our EV6 slow driving noise.

 

Manual specifically states to press the brake petal gently after driving in rain to dry it to avoid rust. Doesn't make sense to me since it would just get wet again instantly. My brakes get used often on hills. The car slams on the brakes in B-mode to avoid rollback on hills. And I live in Northwest Florida where the hills are still very flat compared to Colorado.

I was looking in the manual where it stated D and B give the same recouperation for the same deceleration. I couldn't find it, but we all know the manual is missing all the good stuff. Really doesn't matter since I like B-mode, but would like to know the reference or test data. I do agree in worst case it would be splitting hairs even in heavy stop and go. The only reason I doubt it is from anoadotal evidence of brake dust I get in D mode with low recouperation vs B-mode. It appears to be impossible to determine when the phyiscal brakes kick in during the blend without a BMW Engineer telling you. BMW is so good at the brake petal, I cannot even tell the difference in recouperation on a full battery vs empty, but my battery is very rarely at 100% so haven't tested much. If someone has the brake blending reference off hand, great, if not doesn't matter.

 

Manual specifically states to press the brake petal gently after driving in rain to dry it to avoid rust. Doesn't make sense to me since it would just get wet again instantly. My brakes get used often on hills. The car slams on the brakes in B-mode to avoid rollback on hills. And I live in Northwest Florida where the hills are still very flat compared to Colorado.

I was looking in the manual where it stated D and B give the same recouperation for the same deceleration. I couldn't find it, but we all know the manual is missing all the good stuff. Really doesn't matter since I like B-mode, but would like to know the reference or test data. I do agree in worst case it would be splitting hairs even in heavy stop and go. The only reason I doubt it is from anoadotal evidence of brake dust I get in D mode with low recouperation vs B-mode. It appears to be impossible to determine when the phyiscal brakes kick in during the blend without a BMW Engineer telling you. BMW is so good at the brake petal, I cannot even tell the difference in recouperation on a full battery vs empty, but my battery is very rarely at 100% so haven't tested much. If someone has the brake blending reference off hand, great, if not doesn't matter.

If you press the brake pedal gently it won't apply friction brakes! I think they have copy pasted this from their ICE cars!

 

I think it self-cleans after the car goes through a puddle of water (not sure how it knows) or maybe if it rains (wipers on).

 

I think that this is definitely not the case because if it was then I would be driving constantly with the brakes applied...

 

I see that bar go gray all the time, and have asked the question before. I do believe that it just means maximum regen braking is exceeded.

 

First I've heard of this!!
Now I gotta go try it.

 

I noticed that sometimes (usually when I slam the brakes) the regen meter on the dashboard goes all way down and fades to black. It's either maximum regen, or maybe (my guess) a sign that non-regen braking is engaged.

 

On my M50 brakes never needed cleaning. I did drive it conservatively a while so no friction brakes really used for day to day driving. Let’s remember that friction brakes are engaged every time the car is stopped, even in B-mode (OPD).

I'm sure it does its own brake maintenance, at least on my M50, and you never have to brake hard or do other silly things like that to use the brakes. As with most i4 things, my evidence is anecdotal

 

Yes. The only way we could really get evidence of this if we could check the code controlling the handling of brakes.

I know that the friction brakes are applied even in B but if you drive on a flat road and lift your foot slowly, it will only be set when the car is stopped, and that won't clean the brakes.

 

I wasn't aware that could happen, I just checked my rotors and I see mini pits everywhere ahaha so I guess it's a real EV concern, at least for smooth braking drivers.

 

If you aren't braking hard enough to occasionally engage the physical brakes then you aren't allowed to buy an M50.

Once you have had the M50 a while, it would be interesting to hear your thoughts on the comparison. The car I was originally going to buy was a Polestar 2 but when I eventually got to ride along with someone local (165 miles to nearest test centre), I felt it was a bit meh. I really didn't want spend as much as £50,000 on a car...so I spent £70,000 instead 😖

 

So my question is, does anyone know for certain whether braking on the i4 is also a hidden combination of regen and physical braking? I'm thinking that if BMW use permanent magnet motors in the i4, then actually it would have to be, due to the basic physics of electromagnetism.

I don't know the Polestar but the i4 is using blended braking, it uses regen as long as it is possible. Rust can build up on the disks, but that's easy to get rid of, just slam on the brake pedal a few times when you see traces of rust. No big deal. Of course, you should not do this on a road with traffic behind you. Anyway, this is not EV specific, you can get rust on the disks even in an ICE if you are not an aggressive driver and not race between traffic lights.

 

Thanks for all the replies!

 

Perhaps a better way of understanding it is that for any given rate of deceleration, the amount of recuperation will be identical no matter what driving mode is set.

 

I think I understand what you guys are saying in how it should work. I guess I just can't believe it's always going to come out perfectly the same. Maybe I am splitting hairs.

"Obviously if you’re better at gradually stopping the car using the brake pedal vs in B mode (or vice versa) for example, you’ll add more power back to the battery. "
If you are saying that you can regain more energy using one method vs the other, then you are proving my point!

Anyway I think OP got his answer and this is a tangent. Until we see data we can just all agree the brakes work quite well

 

Think of it this way. Let’s say you’re going 60mph and you come to a gradual stop in 200 feet. Same amount of energy will be recuperated regardless of D (any setting) or B mode. This is the nature of the i4 blended brakes. The car will first use recuperative braking to slow the car, and if that is insufficient the friction brakes will engage.

If the gradual stop is identical (meaning you stop the car at the exact same rate) in any of the D modes or B mode, then you’ll get an identical amount of power going back to the battery.

Obviously if you’re better at gradually stopping the car using the brake pedal vs in B mode (or vice versa) for example, you’ll add more power back to the battery.

 

Yes it uses blended braking.

And I think those of us who were lucky enough to do a PCD can tell you how excellent the car performs under hard braking situations as well as what most of us experience in day to day driving.

 

Neither the brake pedal or accelerator directly control things they are both fly by wire to a computer. Therefore, the movements you do on the pedals can all be translated into exactly the same resultant blend of recoup/friction. If you threshold brake, to create the same amount of braking force in B mode you would also have to press the brake pedal (thereby applying the friction pads given that max recoup has been used in the removal of your pressure on the accelerator). No different to using, say, Low in D and applying the brake pedal to achieve the same threshold braking affect you are after.

 

They can be a lot of variation in how the pedal is applied - or not applied. Say I threshold brake, converting more energy into heat via the rotors/pads. Then I almost coast, barely lifting the throttle, until the car stops in B mode.
Then I do this in every mode and all the recuperative level settings.

I totally buy it being close, but identical? Dunno.

 

It's not hidden. The blended braking is stated clearly in the Owners Manual.

The car seems to have no issue keeping the brakes clean. My TM3 would get rust appearing pretty regularly, but I've seen none at all on my i4 in a year and a half.

 

It's not hidden. The blended braking is stated clearly in the Owners Manual.

The car seems to have no issue keeping the brakes clean. My TM3 would get rust appearing pretty regularly, but I've seen none at all on my i4 in a year and a half.

The car doesn't clean the brake disks automatically. If you never get any rust then you are driving harder than I do. My brakes need a "cleaning braking" now and then. I am also mostly using OPD so my friction brakes aren't used that often.