Regeneration brake light

[Kithmo]

We need a bumper sticker...

(not my spelling of sudden)

 

[Adee]

What's good for the goose is good for the gander, surely? If the SUV had brake lights on regen then the MG5 ought to have the same? When I use KERS3 (all the time obviously ), I feel distinctly exposed knowing that the brake lights are not coming on when I take my foot right off the "throttle". I'm sure there will be ramifications (or hopefully an upgrade) in the weeks to come. On the positive side, it does encourage you to anticipate the need to slow down and use the KERS more sensitively (which keeps miles/kWh up as well).

 

[Lucky5]

The MG5 most likely does not exceed the figure for deceleration set in law to require the use of auto brake lights. No diesel/petrol car does either if you let off the accelerator they decelerate pretty quickly in lower gears with no brake lights. This is why drivers are supposed to leave a gap to the car in front so they have time to stop if the car in front slows and not tailgate you so you can see the whites of their eyes. MG5 only has slightly stronger regen than our older leaf so I don’t think there is an issue personally but what do I know I guess without being able to accurately measure the maximum rate of deceleration it can achieve in Kers 3

 

[Adee]

I take all your points Lucky and I agree that safe driving (i.e.leaving a decent gap in front etc) should be practised by all. There may be a law governing deceleration rates but I very much doubt it. I say this because some brake pedals cause the brake light to come on before any actual braking effort is applied so there can't be any correlation between braking effort and brake light illumination in law. But to me it is just common sense - err on the safe side etc. Car manufacturers keep missing opportunities for safety (in the interests of fashion) and I would cite in particular the embedding of indicator light into headlight clusters. It's so easy to not spot an oncoming car indicating these days. Or maybe I'm just getting old, cranky and poor-sighted

 

[Petriix]

I take all your points Lucky and I agree that safe driving (i.e.leaving a decent gap in front etc) should be practised by all. There may be a law governing deceleration rates but I very much doubt it. I say this because some brake pedals cause the brake light to come on before any actual braking effort is applied so there can't be any correlation between braking effort and brake light illumination in law. But to me it is just common sense - err on the safe side etc. Car manufacturers keep missing opportunities for safety (in the interests of fashion) and I would cite in particular the embedding of indicator light into headlight clusters. It's so easy to not spot an oncoming car indicating these days. Or maybe I'm just getting old, cranky and poor-sighted

There objectively is a law about brake lights and deceleration. Brake lights are normally mechanically triggered by the action of using the brake pedal, so it's obviously going to work differently to the calculated deceleration rate from regen. It's possible that MG have simply taken the upper limit as the trigger point but I wouldn't put it past them to have written some dodgy software that doesn't quite conform to our expectations.

The simple solution is to slightly depress the brake pedal whenever you believe the brake lights should be on, especially if there's someone close behind you. A small amount of force on the pedal will simply apply a tiny bit more regen anyway so it won't cost you anything in the way of energy anyway. You should be paying attention to your mirrors and making constant choices about how to drive appropriately and this is no more than a pragmatic approach to keeping everyone safe. I guess I err on the side of driver responsibility rather than expecting my car to do it for me.

 

[Kithmo]

I usually stomp on the brakes, AKA do a brake check, when there's someone close behind.
I don't really, but I will slow down if some one is tailgating, mainly to let them pass. If they don't pass when the opportunity arises then I just keep driving slow or pull over.

 

[Lucky5]

As above really, if someone seems to close behind then you have to leave an extra gap in front so if you have to stop you can hopefully do so more slowly saving their bacon! Normally I stop gently anyway even if in Kers 3 as it is more efficient to regen at a lower level and longer due to losses at higher power I guess, so the only time it will ever be an issue is in a real emergency and then brake lights will definitely be on and if they end up stuck on the back window then it is their fault. I will however be pretty hacked off in this event as the 5 will probably be my one and only new car experience. It feels like I am tailgated less since removing the EV badge as well. Before the 5 it felt the same when comparing driving in my focus compared to the Leaf that people really tried to push you along in the leaf...Probably all in my head though Ha Ha!

 

[rogerco]

In the previous thread on this topic (which apparently wasn't the first) the consensus was that the (legal?) requirement is that the brake light must be on if the deceleration is greater than 0.3g (or an acceleration of -0.3g if you prefer)

0.3g implies, your car should decelerate by 10.5kmph or 4.07mph every second. Which means car at 60mph should come to standstill in 15 seconds.

That is probably more than you'll get from KERS3 on its own in most circumstances

 

[Adee]

Well 0.3g (wherever that came from?), does equate to 10.5kph per second as stated by LeoRBK, but that actually equates to 6.62mph per second (rather than the figure of 4.07, as quoted). So that's 60 to 0 in 9secs, or 30 to 0 in 4.5 secs. I haven't (yet) put it to the test but I would be surprised if the KERS3 setting doesn't come close to that figure of 4.5sec from 30mph. Importantly, though the deceleration with KERS is non-linear (i.e it's greatest at the point you first take your foot off the accelerator - an obvious point as the car never reaches 0mph without using the brake). So it would be more appropriate to be looking at, say, a 30 to 20 deceleration time of 1.5 secs as the benchmark. I'm sure it'll be close to this (assuming this is a legal requirement and not a figure pulled out of the air?).

 

[Adee]

An update for anyone who is interested......

I have an old G-Tech accelerometer which I have just used to test the deceleration under KERS3. It is typically around -0.15g but did flash as high as -0.17. This was more or less what I expected after counting seconds in my head between 10mph increments (3-4secs) earlier in the day. The battery charge was about 60% at the time and my headlights were on (I think the load makes a small difference). Deceleration is relatively linear with time over the range 60mph to 20mph. I did the test on a fairly flat road. There may easily be variability between vehicles and conditions, but it's unlikely it will exceed -0.3g under any circumstances. I'd still like to know where this number comes from and I still think the brake light should come on under KERS3. I'm not worried by good and careful drivers like us lot - it's the others that worry me!!

And the question you are all asking now......how fast did it accelerate? In Sport Mode it peaks at 0.45g at take off, but drops with speed to around 0.25g at around 60mph. I would attribute the fall-off to wind resistance and other drag factors but it could be related to the motor characteristics as well and maybe transmission drag. I don't know a lot about this technology.

We know that 0.3g corresponds to an accel/decel of about 60mph in 9 secs (see earlier in the thread). So 0.45g would equate to approx 0-60 in 6secs. But, as observed, it can't keep this up so the quoted 0-60 time of around 7.5 seconds seems about right. It also confirms that the accelerometer is in the right ball-park at least.

 

[Adee]

And, I have uncovered a reference to this document which may or may not be up-to-date:

https://unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/R13hr2e.pdf

Within it is the following para....

5.2.22.4. Electric regenerative braking systems as defined in paragraph 2.17., which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions:
Vehicle decelerations
≤ 0.7 m/s² The signal shall not be generated

0.7 m/s² and ≤ 1.3 m/s² The signal may be generated
1.3 m/s² The signal shall be generated

I would reiterate that I have no idea if these are currently considered as legal requirements but at least they provide indicative guidelines.

It states that the (braking) signal must be produced for a deceleration of >1.3m/s/s. This equates to 1.3/9.8 = 0.13g. So, according to my measurements (0.15g), the brake light should be applied????

Teslas and MG SUVs have brake lights activated by regen. Why not the MG5??

 

[Jomarkh]

I found this site might get a few for the rear bumper or window

 

[Jocko]

I can remember when cars with disc brakes would display a sticker to that effect.


https://www.picclickimg.com/d/l400/...-Original-Vintage-Discs-Brake-Warning-Car.jpg

 

[rogerco]

I can remember when cars with disc brakes would display a sticker to that effect.

And lorries had signs saying "Warning Air Brakes" which really puzzled me as a child - how can air be used to brake a big lorry? (no need to answer - I'm older and maybe wiser now).

 

[rogerco]

It seems that there is nothing in the latest amended 1989 Road Vehicles Lighting Regulations so it is not yet a legal requirement in the UK.
However there is reported to be both EU and UN recommendations relating to the 1.3m/s/s - naturally neither of those affect us here in the UK because we live in a parallel universe.

 

[nicko1]

I have switched my mg zs ev for the mg5 ev, happy with the mg5 but unlike the mgzs ev I don't think the brake lights come on with heavy regeneration had anyone else noticed this,is it normal or is there a fault.

why you switch from beauty to ugly ?

 

[GordieG]

why you switch from beauty to ugly ?

You’ll get monstered for posting on the MG5 forum.
Oops, me too!

 

[Adee]

why you switch from beauty to ugly ?

Beauty is in the eye of the beholder. As far as I'm concerned most "modern" cars are pretty ugly, it's just a matter of picking the least ugly.

 

[Scorpion]

I found this site might get a few for the rear bumper or window

I'm going for an AUDI stuck on my rear bumper

 

[Adee]

I'm going for an AUDI stuck on my rear bumper

Well unless they get this regen brake light working I reckon we're all going to get some kind of vehicle stuck on the rear bumper. Just hope it's not a juggernaut.