Electric vehicle queries

[richlist]

What happens with vehicles where the driver turns on the cruise control and the vehicle encounters a downward slope. The vehicle cruise control then slows the vehicle to maintain the cruise setting. Are the brake lights activated ?

[staffordian]

What happens with vehicles where the driver turns on the cruise control and the vehicle encounters a downward slope. The vehicle cruise control then slows the vehicle to maintain the cruise setting. Are the brake lights activated ?

I've never had a cruise control that uses the brakes. Even the speed limiters I've had only control the throttle and will allow overspeeding (with audible warnings) on a downward slope.

But surely if an ICE car has the facility for cruise control to apply the brakes then the brakes lights will come on when the brakes are activated, and with an EV the criteria mentioned above regarding rate of deceleration would determine whether or not the brake lights came on?

[bungeejumper]

I have driven many BEVs over the past few years and none of them illuminated their brake lights when "no longer actively accelerating". The lights only came on when they were braking. The braking force came from either the physical brakes or the engine braking. On the flat this meant the car was slowing down, going down hill it meant the driver was keeping the car under control.

I'm pretty sure we've had a discussion on this forum about EV brake lights coming on during regenerative braking, although I think that particular instance was with a hybrid. In the meantime:
https://www.consumerreports.org/cars/ca ... 20insights.

“On average, we found that the brake lights of most EVs in our fleet illuminate when the regenerative braking system is slowing the car at about 0.1 g (g-force), which could be described as a slight but noticeable amount of braking force,” says Alex Knizek, CR’s manager of auto testing and insights.

BJ

[Niksen]

What happens with vehicles where the driver turns on the cruise control and the vehicle encounters a downward slope. The vehicle cruise control then slows the vehicle to maintain the cruise setting. Are the brake lights activated ?

Probably not as the car isn't decelerating and is just maintaining its speed.

If the car is decelerating under cruise control then the brake lights will illuminate, which is rather helpful as my car which has adaptive cruise control leaves it very late before decelerating.

if you are approaching a roundabout on a dual carriageway at 70mph with stationary traffic ahead waiting to join the roundabout, the car will barrel along at 70mph until almost the last possible moment before using significant regeneration to slow rapidly. Rather unnerving the first time you encounter it and think that the car hasn't seen the traffic ahead.

[DrFfybes]

if you are approaching a roundabout on a dual carriageway at 70mph with stationary traffic ahead waiting to join the roundabout, the car will barrel along at 70mph until almost the last possible moment before using significant regeneration to slow rapidly. Rather unnerving the first time you encounter it and think that the car hasn't seen the traffic ahead.

I must admit I would never have let a driver assistance feature get me into that position in the first place. If the road is wet and oily does it react sooner? If your lane is clear but the other lane is stationary does it still barrel past at 70?

Paul

[88V8]

I have driven many BEVs over the past few years and none of them illuminated their brake lights when "no longer actively accelerating". The lights only came on when they were braking. The braking force came from either the physical brakes or the engine braking.

I'm pretty sure we've had a discussion on this forum about EV brake lights coming on during regenerative braking, although I think that particular instance was with a hybrid. In the meantime:
https://www.consumerreports.org/cars/ca ... 20insights.

“On average, we found that the brake lights of most EVs in our fleet illuminate when the regenerative braking system is slowing the car at about 0.1 g (g-force), which could be described as a slight but noticeable amount of braking force...

I wonder if this will have to be part of the MOT test. How could it be tested, other than on the road with a follower?

V8

[staffordian]

I'm pretty sure we've had a discussion on this forum about EV brake lights coming on during regenerative braking, although I think that particular instance was with a hybrid. In the meantime:
https://www.consumerreports.org/cars/ca ... 20insights.

I wonder if this will have to be part of the MOT test. How could it be tested, other than on the road with a follower?

V8

I would imagine that the rollers used for testing the brakes could be reprogrammed to include such a test if it were to be part of the MOT.

[bungeejumper]

if you are approaching a roundabout on a dual carriageway at 70mph with stationary traffic ahead waiting to join the roundabout, the car will barrel along at 70mph until almost the last possible moment before using significant regeneration to slow rapidly. Rather unnerving the first time you encounter it and think that the car hasn't seen the traffic ahead.

LOL, if you find that hard stop unnerving in your modern car, spare a thought for the driver right behind you in an elderly Skoda, or maybe a Citroen 2CV with drum brakes all round.

Or my 1970s Fiat 500, which had the same puny braking power. Not to mention my former neighbour's vintage Bugatti...

BJ

[88V8]

I wonder if this will have to be part of the MOT test. How could it be tested, other than on the road with a follower?

I would imagine that the rollers used for testing the brakes could be reprogrammed to include such a test if it were to be part of the MOT.

The brake rollers at my MOT garage are analogue. I'm sure they wouldn't work in reverse.

The latest rumour is that new cars will have an 'MOT chip' such that they will be disabled if certain safety-critical functions are disfunctional. Big Brother is coming.

V8

[Oggy]

Big Brother is coming

He's already here. Have you seen the numbers of cameras in our towns and cities? All for our safety naturally - and that must be right as it comes directly from the Ministry of Truth.

[Niksen]

if you are approaching a roundabout on a dual carriageway at 70mph with stationary traffic ahead waiting to join the roundabout, the car will barrel along at 70mph until almost the last possible moment before using significant regeneration to slow rapidly. Rather unnerving the first time you encounter it and think that the car hasn't seen the traffic ahead.

I must admit I would never have let a driver assistance feature get me into that position in the first place. If the road is wet and oily does it react sooner? If your lane is clear but the other lane is stationary does it still barrel past at 70?

To be honest I now flick off the cruise control as I approach the roundabout and then let the automatic regeneration slow instead, as that is more like coasting and then the car applies a more gentle deceleration as we approach the stationary traffic.

However to answer your questions, no it doesn't react sooner if the road is wet but you can manually alter the distance that you are following another vehicle when the cruise control is on in four steps ranging from the distance that most people would leave on a motorway, i.e. too close, to the sort of distance you want in the rain.

And if the other lane is stationary, then yes it will continue to barrel along at full speed irrespective of that stationary traffic, and that is why I now flick it off as I want to avoid the possibility of someone fulling out of that stationary lane not expecting two tonnes of SUV to be heading towards them at 70mph.

LOL, if you find that hard stop unnerving in your modern car, spare a thought for the driver right behind you in an elderly Skoda, or maybe a Citroen 2CV with drum brakes all round.

Unless they are Mr Magoo and can't see the stationary traffic ahead then I think their nerve would give out way before there was an issue!

[Arborbridge]

I find the ACC* a very useful device, especially in heavy/slow traffic. It works really well, but like all these things one has to be aware of how it works and what the limitations are (eg at roundabouts!). One interesting thing is that the distance one can set to the vehicle in front seems to be dynamic - that is, it will depend on speed, so in slow traffic it will bunch up more to the car in front just as a human driver would.

Ultimately, the drive is in charge and it is your own responsibility to drive safely. The ACC is a useful aid and can be altered or overridden immediately with a tap on one pedal or the other. That being so there is no excuse to "let a driver assistance feature get me into that position in the first place." If one is driving with due care and attention, that will never happen.

Arb.

Adaptive cruise control, not assistant chief constable!

[quelquod]

I've never had a cruise control that uses the brakes. Even the speed limiters I've had only control the throttle and will allow overspeeding (with audible warnings) on a downward slope.

But surely if an ICE car has the facility for cruise control to apply the brakes then the brakes lights will come on when the brakes are activated, and with an EV the criteria mentioned above regarding rate of deceleration would determine whether or not the brake lights came on?

My last 3 cars (all BMWs) have applied the (rear) brakes as necessary during cruise control to prevent overspeeding. The braking is applied early enough that I doubt the minimal deceleration needed would trigger the brake lights. This is as opposed to the alternative speed limiter which does allow overspeeding (and which I generally prefer to use to keep rear brake wear down and which practically speaking emulates what most drivers would normally do excepting in extreme downhill cases). The situation is different if the car brakes automatically due to traffic conditions whether in cruise or not.

[swill453]

My last 3 cars (all BMWs) have applied the (rear) brakes as necessary during cruise control to prevent overspeeding. The braking is applied early enough that I doubt the minimal deceleration needed would trigger the brake lights. This is as opposed to the alternative speed limiter which does allow overspeeding (and which I generally prefer to use to keep rear brake wear down and which practically speaking emulates what most drivers would normally do excepting in extreme downhill cases). The situation is different if the car brakes automatically due to traffic conditions whether in cruise or not.

Do you really mean "rear" braking? I would have thought it would be pretty unstable/dangerous to only brake the rear wheels.

Scott.

[richlist]

Picture the scene ......I'm in my Mercedes, I've set the cruise control at say 50mph and then find I'm rapidly approaching a 30 mph section of road. Instead of switching off the CC / braking, I can operate the cruise control in 5mph jumps. So, I hit the CC x4 times in quick succession. The car rapidly slows to 30mph and I can't see any way it can do it that quickly without operating the brakes.

[9873210]

I wonder if this will have to be part of the MOT test. How could it be tested, other than on the road with a follower?

If you need to:
Ditch the follower, suction cup a camera on a stick to the fender during the test drive.

A cheap cell phone could automate the whole test. Camera, accelerometer, enough CPU for processing, and connectivity included. Cost of software would be small if amortized across a few million MOTs. Might have to retire a few mechanics that think carburetors are state of the art but there canu't be many of them left.

[quelquod]

My last 3 cars (all BMWs) have applied the (rear) brakes as necessary during cruise control to prevent overspeeding. The braking is applied early enough that I doubt the minimal deceleration needed would trigger the brake lights. This is as opposed to the alternative speed limiter which does allow overspeeding (and which I generally prefer to use to keep rear brake wear down and which practically speaking emulates what most drivers would normally do excepting in extreme downhill cases). The situation is different if the car brakes automatically due to traffic conditions whether in cruise or not.

Do you really mean "rear" braking? I would have thought it would be pretty unstable/dangerous to only brake the rear wheels.

Scott.

Nevertheless I believe it’s the case that only rear braking is used by BMW cruise control, it’s well documented in the user forums, you can feel the car ‘squatting’ slightly as it engages, and drivers who routinely use cruise control have reported slightly higher rear brake wear. It’s a mild control to handle normal road undulations, not full on braking as for auto distance control.

[Watis]

My last 3 cars (all BMWs) have applied the (rear) brakes as necessary during cruise control to prevent overspeeding. The braking is applied early enough that I doubt the minimal deceleration needed would trigger the brake lights. This is as opposed to the alternative speed limiter which does allow overspeeding (and which I generally prefer to use to keep rear brake wear down and which practically speaking emulates what most drivers would normally do excepting in extreme downhill cases). The situation is different if the car brakes automatically due to traffic conditions whether in cruise or not.

Do you really mean "rear" braking? I would have thought it would be pretty unstable/dangerous to only brake the rear wheels.

Scott.

As a cyclist - and then a motorcyclist - back in the day, I was taught to apply the rear brake before the front brake for improved stability.

Watis

[swill453]

Do you really mean "rear" braking? I would have thought it would be pretty unstable/dangerous to only brake the rear wheels.

As a cyclist - and then a motorcyclist - back in the day, I was taught to apply the rear brake before the front brake for improved stability.

Me too, but I was also told never to use the handbrake as an "emergency" brake in a car as it may cause loss of control.

Scott.

[88V8]

My last 3 cars (all BMWs) have applied the (rear) brakes as necessary....

Do you really mean "rear" braking? I would have thought it would be pretty unstable/dangerous to only brake the rear wheels.

Until the mid-20s, cars only had rear brakes.
The Model T Ford - 15mio produced - never had front brakes.

V8