No brake llights above 136 kph (85 mph) while using regen braking

[Daniel 74]

Hi Saul, nice to meet you here!
This issue has been discussed in the Dutch and Belgium part of this forum. We came to the conclusion that none of the classic model s'es have braking lights going on with full regen at high speeds.

This seems right, as the deceleration from regen is relatively low at high speeds.

 

[FlatSix911]

To slcuervo: have you been able to ascertain your claim by having another tail you and let you know yea/nay wrt your brake lights? I would wonder if any problem that might exist COULD be solely in the dashboard display. To the overall point, however: I would suggest that any responsible driver who is interested in decelerating a vehicle going 135kph/85mph....should very most definitely make use of the brake pedal.

Another method to confirm the rear brake light operation is to turn on the rear view camera while at speed.

 

[slcuervo]

Another method to confirm the rear brake light operation is to turn on the rear view camera while at speed.

I'll try that, but I think I am not able to see any light coming from the brake lights through the rear view camera... What should I be looking for? In what area should I see it?

 

[slcuervo]

when you lift your foot in the limiting case of extremely high speed, a Tesla with regen won't decelerate at a significantly higher rate than an ICE car, even though the absolute deceleration of both is high due to air drag. Since it's okay for ICE cars not put on the brake lights upon lifting at high speed, Tesla's thought must be that it's also okay for a MS, which would only be decelerating at a slightly higher rate.

This would be the ultimate test for me. If I had a way to take a friend with me on a German highway, each on his car, we could test this.

We would both cruise at high speed (say 100 mph), the Model S would be ahead and would lift the foot off at a certain point.
The ICE, following at safe distance, would lift the foot as well, and compare. If his deceleration rate is lower and he is forced to step on the brake to equal the Model S deceleration, then my assumption is right and the way brake lights behave under regen at high speed is wrong. If his deceleration is equal to or greater than the Model S, I'll shut up

But this is not easy to do in Norway with our very low speed limits...

 

[slcuervo]

To slcuervo: have you been able to ascertain your claim by having another tail you and let you know yea/nay wrt your brake lights? I would wonder if any problem that might exist COULD be solely in the dashboard display.

.

No, unfortunately not. I am assuming the toy car displays what the actual car does.

- - - Updated - - -

Hi Saul, nice to meet you here!
This issue has been discussed in the Dutch and Belgium part of this forum. We came to the conclusion that none of the classic model s'es have braking lights going on with full regen at high speeds.

This seems right, as the deceleration from regen is relatively low at high speeds.

I guess it´s all in Dutch, so I won´t bother you with passing me the link :tongue:

Could you however say if someone has tried what I have posted above? 2 cars, a Model S and an ICE cruising at the same speed and both lifting the foot off? Do you know?

 

[MikeC]

I'll try that, but I think I am not able to see any light coming from the brake lights through the rear view camera... What should I be looking for? In what area should I see it?

At night when it is dark you can see the red light on the backup camera screen.

 

[AWDtsla]

This would be the ultimate test for me. If I had a way to take a friend with me on a German highway, each on his car, we could test this.

We would both cruise at high speed (say 100 mph), the Model S would be ahead and would lift the foot off at a certain point.
The ICE, following at safe distance, would lift the foot as well, and compare. If his deceleration rate is lower and he is forced to step on the brake to equal the Model S deceleration, then my assumption is right and the way brake lights behave under regen at high speed is wrong. If his deceleration is equal or greater to the Model S, I rest my case.

But this is not easy to do in Norway with our very low speed limits...

What gear is the ICE in? Does it have a locking torque converter? Does it have a V8 or and I4 or other? Does it have a high drag coefficient and area? What brand are the tires? Are they new? Does the ICE have it's windows open?

We can make your test go anyway we want, easily...

 

[Daniel 74]

No, unfortunately not. I am assuming the toy car displays what the actual car does.

- - - Updated - - -



I guess it´s all in Dutch, so I won´t bother you with passing me the link :tongue:

Could you however say if someone has tried what I have posted above? 2 cars, a Model S and an ICE cruising at the same speed and both lifting the foot off? Do you know?

It will depend on the type of ICE one would use in this test. I'm pretty sure that if my landrover defender 110 is used, it will decelerate more than the tesla using full regen [emoji16].

Of course, this is highly theoretical: my defender doesn't go faster than 130 km/h [emoji12].

Thinking of it, even at that speed it will decelerate faster... It all depends on the drag of the car, and you can't do worse than the brick on wheels the defender is.

Here's the link: Bij classic Model S remlichten niet actief boven de 136 km/u bij regen remmen

 

[ecarfan]

I'll try that, but I think I am not able to see any light coming from the brake lights through the rear view camera... What should I be looking for? In what area should I see it?

At night it is easy to see the red glow of the brake lights in the rear view camera image.

 

[sillydriver]

This would be the ultimate test for me. If I had a way to take a friend with me on a German highway, each on his car, we could test this.

We would both cruise at high speed (say 100 mph), the Model S would be ahead and would lift the foot off at a certain point.
The ICE, following at safe distance, would lift the foot as well, and compare. If his deceleration rate is lower and he is forced to step on the brake to equal the Model S deceleration, then my assumption is right and the way brake lights behave under regen at high speed is wrong. If his deceleration is equal to or greater than the Model S, I'll shut up

But this is not easy to do in Norway with our very low speed limits...

I think this test should have the ICE car in a lower gear where RPMs are high, not in the highest possible gear which would be used for cruising at high speed. The reason is that it is considered legal for ICE cars to decelerate under engine braking in any gear without having their brake lights on. Then it should be legal for a MS to decelerate at that same rate without brake lights.

I am jealous of European opportunities to cruise legally at 100 MPH!

 

[slcuervo]

I am jealous of European opportunities to cruise legally at 100 MPH!

Only in Germany, the rest of Europe has limits around 70-80 mph

- - - Updated - - -

I think this test should have the ICE car in a lower gear where RPMs are high, not in the highest possible gear which would be used for cruising at high speed.

Totally agree. Too bad I couldn´t try that with someone else driving an ICE car...

I hope someone reads this thread in (or close to) Germany and takes the time to do the test!

 

[Cottonwood]

Pretty simple equations:

• Power = Force * Speed
• Acceleration = Force/Mass
• Acceleration = Power/Speed/Mass

This morning because of a cold battery, my regen was limited to 25-30 kW (hard to be precise with new display) in my P85D. I started at 55 mph, and let off the accelerator to get max regen. There were no brake lights until I slowed down to 38 mph. That seem to correlate with the full regen and 85 mph threshold of the OP.

It seems that the brake lights are triggered when the regen deceleration is above some threshold. As speed increases, regen deceleration decreases. The brake lights are triggered by using the brakes or enough regen deceleration. The lights are not triggered by aerodynamic deceleration or grade induced deceleration.

 

[sorka]

Sorka -- interesting data on these deceleration rates.

As you say, the force and hence the contribution to deceleration (in Gs) of air drag goes as v^2. On the other hand, the contribution to deceleration (in Gs) of the maximum regen level in kW goes as 1/v. The point is, the higher the speed, the lower the contribution of regen as a % of total deceleration when you lift. I suspect the brake lights don't go on unless either the total Gs due to regen is over some threshold, or the percentage of the total deceleration due to regen is over some threshold, neither of which condition can be met at very high speed. Why is this okay? Because when you lift your foot in the limiting case of extremely high speed, a Tesla with regen won't decelerate at a significantly higher rate than an ICE car, even though the absolute deceleration of both is high due to air drag. Since it's okay for ICE cars not put on the brake lights upon lifting at high speed, Tesla's thought must be that it's also okay for a MS, which would only be decelerating at a slightly higher rate.

My point is it shouldn't matter what the cause of deceleration is. If it goes beyond a certain threshold g-force the brake lights should come on. Regular ICE cars don't or at least don't yet(some are starting to) because they've traditionally used a switch on the brake pedeal. The advent of cheap solid state accelerometers will change all of that.

On the other hand, if you're the type to not want to get caught speeding and feel that keeping the brake light from coming on by downshifting several gears will save you, then fine. I just don't want to get rear ended while doing that because my brake lights didn't come.

 

[jpet]

@slcuervo, we've got confirmation now from several European drivers that have tested this strange behavior. So it is not your car. All non auto-pilot cars seem to behave this way. I assume it's a bug since why would this be limited to non-autopilot cars? In mine the brake lights come on at any speed when regen goes above approximately 30 kW.

 

[sillydriver]

My point is it shouldn't matter what the cause of deceleration is. If it goes beyond a certain threshold g-force the brake lights should come on. Regular ICE cars don't or at least don't yet(some are starting to) because they've traditionally used a switch on the brake pedeal. The advent of cheap solid state accelerometers will change all of that.

On the other hand, if you're the type to not want to get caught speeding and feel that keeping the brake light from coming on by downshifting several gears will save you, then fine. I just don't want to get rear ended while doing that because my brake lights didn't come.

I think you have a reasonable view about what the role of brake lights should be, but that is not what their role actually is for any of the cars currently on the road. So what I was trying to address is whether the brake lights on Teslas behave similarly to the brake lights on all the other cars.

Before getting the MS I've always liked the pedal feel of ICE cars with heavy engine braking, so I've always bought cars with large engines (2 W12s, a V12, and a few V8s) and tended not to drive in top-gear, even with automatics. One of the reasons I love the MS is that it gives me even more of that deceleration (and as should be clear, I did not buy the MS because I'm big on saving gasoline). The fool-the-cops gambit has never been part of my motivation. Because of all that ICE engine braking (and also because it's the correct way to drive) I'm in the habit of using the mirror to see what's behind me! If I have any concern, such as coasting down toward a back-up on a highway, I tend to multiple-tap the brake to warn those behind.

 

[SlyWombat]

I think you have a reasonable view about what the role of brake lights should be, but that is not what their role actually is for any of the cars currently on the road. So what I was trying to address is whether the brake lights on Teslas behave similarly to the brake lights on all the other cars.

Before getting the MS I've always liked the pedal feel of ICE cars with heavy engine braking, so I've always bought cars with large engines (2 W12s, a V12, and a few V8s) and tended not to drive in top-gear, even with automatics. One of the reasons I love the MS is that it gives me even more of that deceleration (and as should be clear, I did not buy the MS because I'm big on saving gasoline). The fool-the-cops gambit has never been part of my motivation. Because of all that ICE engine braking (and also because it's the correct way to drive) I'm in the habit of using the mirror to see what's behind me! If I have any concern, such as coasting down toward a back-up on a highway, I tend to multiple-tap the brake to warn those behind.

Ditto, I used to drive a manual, and there is no brake light when I downshift, so the fact that Tesla is "signalling" due to deceleration is a bonus, not a requirement (in fact sometimes I think it gives the wrong signal, I might be using switching lanes and letting go of the go button indicates I am slowing down, but in fact I am about to switch lanes and continue the 'go')

 

[jcaspar]

I agree. I don't see where this is an issue given the regeneration has a relatively slow braking effect at any speed. My Gen II Viper with an 8L V-10 would decelerate so fast letting off the gas in second gear you could break the 335 tires loose. No brake lights went on. Never got rear ended.

 

[slcuervo]

I have never said shifting down gears on an ICE produces the same amount of deceleration as the Model S does with full regen (60 kW) at high speeds.

I believe, and this is what my statements and my video are based on, that at speeds above 85-90 mph the Model S decelerates more than most ICEs without using brakes. That is why I uploaded the video.

The fact that other Model S users equipped with AP do have brake lights at those speeds while using regen proves that either my car has a bug, or all classic MS with 7.0 do.

And it also proves my point: deceleration in a Model S is stronger than in an ICE car at high speeds, hence why Model S with AP do have brake lights on when using full regen above 85 mph.

 

[slcuervo]

@slcuervo, we've got confirmation now from several European drivers that have tested this strange behavior. So it is not your car. All non auto-pilot cars seem to behave this way. I assume it's a bug since why would this be limited to non-autopilot cars? In mine the brake lights come on at any speed when regen goes above approximately 30 kW.

Thanks a lot for your work on the other thread!

Very useful inputs. I think I will report this to Tesla. The reason I haven't done it yet is because I am still waiting to see if someone has the opportunity to compare the Model S deceleration at those speeds with that of an ICE car (and check whether the ICE car needs to step on the brake to equal the Model S deceleration with regen or not)...

 

[jerry33]

The fact that other Model S users equipped with AP do have brake lights at those speeds while using regen proves that either my car has a bug, or all classic MS with 7.0 do.

At one time, early on there was a post stating that EU, or at least some EU countries, mandated that the brake lights could only be activated by the brake pedal. I don't know if the regulations changed, or if AP falls under a different set of regulations, but that would explain the difference.