Poor emergency stop

[Rolfe]

I've done it a couple of times in cars with EBA (emergency brake assist) and ABS, braked hard and thought they wouldn't stop.
The EBA works on how fast you press the pedal not how hard.
So if you press the pedal really hard but gradually, the ABS keeps letting the wheels rotate to prevent skidding, whereas if you press the brake fast the EBA kicks in and brakes hard, it is a weird feeling.
When it happens, if you momentarily release the brake then press it again fast the car will stop better.

I just slammed the brake on max as fast as I could on instinct. I got there before the AEB had a chance to engage. I was told very firmly with the first car I had with traction control just to brake as hard as I could and let the traction control system worry about the rest. My stop on Thursday evening was abrupt enough I could believe EBA might have been involved, whatever that is. Either way, the tyres held with no skidding.

Mine did an automated emergency stop a few weeks back when a child with head down looking at a phone just turned and walked out right in front of me about 5m away. Glad the systems worked.

Mine did it a year ago when a man walked into the road from between two parked cars. He wasn't actually in danger, he was heading for the driver's door of one of the parked cars, but I could see why the car wouldn't necessarily have realised that. (I had realised, from his body language.) I thought, well, that was impressive, that could have been a child. So I've never switched the system off, and it's never operated without a reason. I'd hate to switch it off and then have an accident it might have prevented.

 

[Ian Key]

There might have been some surface corrosion on the brake discs which would have decreased the braking efficiency.
I think the AEB system only works if you are not already pressing the brake pedal. If I'm approaching a parked car and have to slow down to wait for an oncoming vehicle to pass and I don't touch the brakes the AEB slams the anchors on, but if I slightly press the brakes it doesn't.

 

[Tuareg]

Maybe you caught the accelerator with the brake pedal?

 

[Flightengineer]

When i first use brakes in slightly emergency situation i was very confused. Brake was very uneffective and pedal feeled spongy. Looking to this forum and it was explained that at new car you should use brakes hard severeal times to adjust disks to brakes. After that looks better but not enough compare to ICE car. Then i realized that, because this electric car dont have vacuum booster for brake system, you just need to push brake pedal harder to get sufficient deceleration, then you use to in regular ICE car.

 

[Spaniard]

One of the things I dislike it the MG4 are the brakes. It's a heavy vehicle, but the touch of the brake does not transmit any confidence at all in any of the modes (comfort, normal or sport) as it does not have the graduality you can find in other cars with that power (>150hp).

I also had to brake hard for first time a week ago and nearly hit the guy preceding because, despite pressing very hard the pedal, it won't stop... then the emergency brake came in and it braked harder enough to avoid the collision. I was on comfort mode... not using it anymore.

 

[Anon70]

This is how the AEB should work, there are 2 settings, warning only and warning with intervention



In this video you can see the slight bend in the road confuses the system as it sees a pedestrian and a van directly in front of the car before the steering wheel has been turned to follow the road

 

[Kithmo]

There might have been some surface corrosion on the brake discs which would have decreased the braking efficiency.
I think the AEB system only works if you are not already pressing the brake pedal. If I'm approaching a parked car and have to slow down to wait for an oncoming vehicle to pass and I don't touch the brakes the AEB slams the anchors on, but if I slightly press the brakes it doesn't.

Just to be clear, I was referring to EBA, emergency brake assist, which comes into effect when you press the brake pedal quickly, not AEB, automatic (or active ?) emergency braking, which is automatic and is overridden by the brake pedal (or the accelerator). Most cars have both these features now.

 

[Anon70]

From a hunt round the internet it seems each manufacture combines their safety systems in different ways.

Kia say this:
"As you may have guessed by its name, AEB works autonomously, with no input from the driver. The system can also add braking force if you are pressing the brake, but weaker than a vehicle needs to avoid a collision."

Telsa did an update to include reversing and higher forward speeds but it can be overridden
"The owner's manual also provides additional information on when AEB does not apply the brakes or stops applying them. These situations include:

• Turning the steering wheel sharply
• Pressing and releasing the brake pedal while AEB is applying the brakes
• Accelerating hard while AEB is applying the brakes
• The detected vehicle, motorcycle, bicycle, or pedestrian is no longer ahead"

Renault also add brake force assistance if you press the brake during a collision detection event
"When the vehicle speed is between approximately 4 mph (7 km/h) and 106 mph (170 km/h), the message “Brake” is displayed in red on the instrument panel 3 accompanied by a beep.

If the driver depresses the brake pedal and the system still detects a risk of collision, the brake force is increased."

But it does have some non activation scenarios...

"Note: if the driver uses the vehicle controls (steering wheel, pedals, etc.) the system may delay certain operations or not activate."

The MG4 manual suggests that brake force is determined by driving mode

IBS can provide 3 different braking response modes for the vehicle:
• Comfort: The braking response is slow and the pedal feel is soft
• Normal: The braking response is moderate and the pedal feel is moderate.
• Sport: The braking response is quick and the pedal feel is sensitive.

It suggests the EBA can increase brake force but does not say how EBA and AEB work together

"The brake system can be divided into service brake system and parking brake system. The service brake system consists of Electronic Brake Force Distribution System (EBD ) and Electronic Brake Assistance System ( EBA ).EBD system can automatically distribute the braking force between the front and rear wheels, so that the vehicle can have good braking performance under different load conditions. The EBA system can increase the braking force applied on each wheel during emergency braking to assist the driver in quickly triggering ABS , thereby shortening the braking distance."

So it looks like the way the systems work is down to the software engineers and how they have coded the systems.

 

[tsedge]

I failed to stop when entering a roundabout behind a driver who changed their mind suddenly. I'm confident that I would have stopped in my last BMW and my wife's Polo, but my MG4 didn’t seem to assist at all, if anything the brakes went a bit spongy. Isn’t it supposed to do emergency stops, even unaided, never mind when the driver is slamming on? What can we expect from the car? Any ideas?

Were you in ECO mode? The pedal takes more pushing for the same effect in this mode. It can sometimes feel like the brakes aren't working well. This is one of the reasons why I drive everywhere in Sport as it has the sharpest response on brakes and accelerator.

 

[Wil Tryharder]

Were you in ECO mode? The pedal takes more pushing for the same effect in this mode. It can sometimes feel like the brakes aren't working well. This is one of the reasons why I drive everywhere in Sport as it has the sharpest response on brakes and accelerator.

This is great information, thank you.

 

[Rolfe]

It's a poor show if ECO mode interferes with an emergency stop though.

 

[pjmmk]

We very rarely come across cars without all sorts of driver aids these days. It's rare for someone to lock up wheels and go skating off into the bushes. The process for emergencies now is to just stamp as fast and as hard as possible on the brake pedal and let the car sort out the mess.
If, after doing that, it fails to stop in a way you think it should, I'd get it to a dealer to check out. You really don't want to be taking chances with defective braking systems.

 

[Rolfe]

Absolutely. Agreed. I did that and my car stopped on a dime. If another MG4 didn't, something is wrong.

 

[YaR]

I'd get your garage to take a look at the brakes, tbh. Regardless of SOC if I brake hard, the brakes grip immediately, there's no sponginess or delayed response.

 

[NLMGSAN]

Were you in ECO mode? The pedal takes more pushing for the same effect in this mode. It can sometimes feel like the brakes aren't working well. This is one of the reasons why I drive everywhere in Sport as it has the sharpest response on brakes and accelerator.

There is no need for that. You can use Custom to chose eco for motor, but use sports for steering and chose a different setting for pedals as well.

It's a poor show if ECO mode interferes with an emergency stop though.

It doesn't on mine. Suddenly appearing traffic jam, though anticipated on time, caused the brakes to fully stop the car....10 mtrs behind the next car. But it worked.

 

[tsedge]

There is no need for that. You can use Custom to chose eco for motor, but use sports for steering and chose a different setting for pedals as well.

Yes indeed. But the other reason I use sport is I like the motor response, more fun. No need for custom.

 

[Soultrappa]

I would 2nd the eco mode check. The brakes need to be pushed so much harder in this mode and does feel spongey. Brakes work great at speed and emergency stopping in sports but are quite harsh when coming to a stop at really low speed like traffic lights.

Normal is OK but also sometimes feels a bit spongey in an emergency situation however all will stop you dead if you stamp hard enough.

I've had the AEB happen twice and both times it was like I'd hit a brick wall (and I know how that feels in a vehicle at low speed from past experience).

I've also had to emergency brake a couple of time manually and was surprised at how well it stopped, including going fast enough to actually skid a bit.

I have been impressed by the brakes in this car for it's weight although I would say I did trust the brakes in my focus st a bit more.

If you are having worries then go to a quiet area and trial them and then take to dealers to test if not feeling confident!

 

[andi]

My wife drives on regen all the time very rearly using brakes. She's done 11k miles.when I get in I reduce the regen to 1. Then the brakes get used. I had a similar situation and realised the discs were not as clean as any one else's. Once I had driven mainly using braking only, they came very sharp and back to where I would call normal.
She does drive slow and round town only.
First time I drove quickly I didn't like the brakes at all. So is it lack of heavy breaking that the car is missing. Once the discs had cleaned up they were brilliant.

 

[Soultrappa]

my muss is exactly the same, but I drive the car mostly so the disks are always clean lol.

she will get 5mkwh where I'll be getting 2.5 if in lucky ?

 

[nexia201]

The aeb is easily activated , even when not needed so i would have complained and put the crash on the dealer unless you totally disabled aeb and put it on warning only as car should hsve stopped even if you didnt touch the brakes.