Brake lights or not…

[Bat66]

OK, had a debate the other night about downhill braking and muppet drivers.

When I was learning to drive the practice was to change down, allowing engine braking to maintain the car speed instead of braking all the time.

Jumping 40 years and moving to today with regen braking and ‘muppet’ drivers who seem to need to see a brake light all the time even if it’s just to maintain the same speed going down hill and not speeding up I had a near miss when on the motorbike when I was still doing the 30mph but hadn’t applied the brakes due to engine braking. My thoughts are I wasn’t slowing the vehicle down so no need to show braking. The Muppet behind instead stated my bake lights were not working (not going to use their actual words here) and thus it was my fault.

So thoughts on a postcard please.. AITAH for not using my brakes to maintain the same speed?

 

[Mondomensch]

I think the reasoning behind engine braking is that using the brakes on a long downhill will heat them up, perhaps to the point of brake failure.

 

[kd7iwp]

Fortunately you're on an i3 forum and region does turn on the brake lights. I find that with my other cars (all stick shifts so they have stronger engine braking) I do this all the time but the braking isn't forceful enough that I would slow down to the point that someone would come close behind me. I think that motorbike driver wasn't paying enough due attention or maintaining a proper following distance.

 

[Mondomensch]

I think Bat66 WAS the motorbike driver...

 

[mojo]

I had a near miss when on the motorbike when I was still doing the 30mph but hadn’t applied the brakes due to engine braking.

It's quite clearly the following driver's fault. There is no requirement in law for a driver to be braking or not braking under any specific set of circumstances. But it is a requirement in law (in every jurisdiction that I'm aware about) for a following driver to be aware of what the driver in front is doing and to act safely - whether they are braking or not.

But on the subject of engine braking, there are differing schools of thought on the subject, and I doubt you will get one "correct" answer.

What I was taught is that under most circumstances, modern car brakes are not likely to suffer from overheating and "fade", and they are designed as a "wear and replace" item. Engines and gearboxes are not, so under most circumstances, braking with the footbrake is preferable to using engine braking - wearing out a disposable set of components rather than an expensive part of the car. The exception is on sustained very steep hills where there is known to be high risk of brake overheating. In some countries, descents that are known to be in this category often include signage saying "engage low gear now" or similar, though of course that varies a lot by region.

To add to what Kd7iwp says: the i3 turns on the brake lights during regen, but only if the rate of deceleration is higher than a specified limit. Light deceleration under regen does not illuminate the brake lights.

 

[alohart]

To add to what Kd7iwp says: the i3 turns on the brake lights during regen, but only if the rate of deceleration is higher than a specified limit. Light deceleration under regen does not illuminate the brake lights.

I've wondered whether when descending a steep decline on which speed is being kept constant by regen only, would the i3's brake lights illuminate as they would in ICE vehicles descending the same decline when braking? I've watched i3's descend a hill where I walk and their brake lights seem to illuminate similarly to ICE vehicles descending the hill. I know that regen would be sufficient to maintain speed on that descent so that friction brakes would not need to be applied to maintain a constant speed. At a constant speed, the rate of deceleration would be 0 but the regen level would be high.

Early on, I read that the i3's brake lights illuminate when the regen power, not the rate of deceleration exceeds a certain value. An i3 owner tested this on a level road and determined that the brake lights illuminated when the illuminated segments on the power gauge moved past the 'G' in "CHARGE" (i.e., more than 2 regen segments illuminated). However, on a level road, an i3 would be decelerating, so which triggered the brake lights, the regen power level or the rate of deceleration?

 

[mojo]

In Europe, the operation of brake lights in EVs is standardised according to section 5.22.2 of UNECE Regulation 13-H.

Apparently this includes a requirement that any deceleration of 1.3 metres per second squared, or greater, must light up the stop lamps.

How well that is implemented on an i3 we don't know! Presumably it relies on an accelerometer somewhere in the car, but how accurate it is and, for example, whether it is "corrected" for slope, is not documented anywhere, as far as I know. In fact I can't figure out in my head whether it would need to be "corrected" in that way or not.

I would expect that there is an equivalent specification covering the USA and probably every other region in the world, and the standards are probably the same everywhere, but... again, I don't know.

 

[eNate]

What I've observed is that any time I'm descending regen only, no accelerator & no brake pedal, my brake lamps are illuminated. Even if I'm descending a steep residential street basically at the speed limit (15-20 I think -- a reasonable speed).

And other than that the brake lamps seem to be tied to rate of deceleration, so off for coasting (unless my foot is completely off the pedal), and off for moderate slowing.

 

[Dutchi3]

The brake lights are tied to a certain treshold of deceleration, according to an accelerometer. So you can descent a hill with regen without engaging the brake lights, if you do not decellerate. Similar to a car that uses engine braking to keep a constant downhill speed.

 

[eNate]

Not if the car is traveling at a constant rate of speed and there are no driver inputs.

The steep residential hill I referenced earlier I drove today then measured. It's a 14% slope, losing 100 ft over a 700 ft run. The i3 descends it at a constant 21 MPH with no accelerator nor brake inputs from me, just "natural" regen.

Despite the constant speed, the brake lamps come on and remain on the entire 23 seconds of this descent.

 

[808i3s]

To the OP regarding safe motorcycle engine braking, I was taught to dab or "flash" the brakes when engine braking to "wake up" inattentive drivers. This is especially helpful at night since motorcycles are hard to pick up visually.

 

[Bat66]

To the OP regarding safe motorcycle engine braking, I was taught to dab or "flash" the brakes when engine braking to "wake up" inattentive drivers. This is especially helpful at night since motorcycles are hard to pick up visually.

I agree with the ‘flash’ if slowing the point was I was is that I maintaining the 30mph not actually slowing down using the engine braking.

I seem to remember there are various settings via BmerCode which can alter the i3’s brake light’s settings.

Again the main question would be if on cruise control and maintaining a speed should we show brake lights for muppets behind or not.

 

[mojo]

Again the main question would be if on cruise control and maintaining a speed should we show brake lights for muppets behind or not.

That's a different question than the one you originally asked.

If cruise control is engaged, you cannot manually choose to flash the brake lights. As soon as you touch the brake pedal, cruise control will disengage. All you can do is accept the way that the car is programmed to use the brake lights while on cruise control.

 

[Whereitis]

I've been wondering about brake light action of my i3 and this thread helps clarify it. But I'll add a question about a different car, the 22 RAV4 Prime SE I recently bought to replace my i3. It has distance-keeping cruise control (non-defeatable, typical Toyota) and I've experienced the car slowing to almost a full stop when the car in front of me did, then re-accelerating to the set speed once that car turned off. At no point did I touch either the gas or the brakes. How can I know when the brakes lights go on in these instances?

 

[eNate]

It has distance-keeping cruise control (non-defeatable, typical Toyota)

If it's like other Toyotas you can hold back the stalk and it'll revert to caveman cruise control.

With the i3 and my ID.4, this question about brake lights came up so I taped an inspection mirror to the back window to monitor the 3rd brake light in an attempt to understand the behavior. My main takeaway is that in both cars the lights illuminate about like I would expect them to. I was more concerned that they might be coming on TOO much, with every little slowdown, and not much annoys me more as a driver than following behind a brake tapper.

 

[Whereitis]

If it's like other Toyotas you can hold back the stalk and it'll revert to caveman cruise control.

With the i3 and my ID.4, this question about brake lights came up so I taped an inspection mirror to the back window to monitor the 3rd brake light in an attempt to understand the behavior. My main takeaway is that in both cars the lights illuminate about like I would expect them to. I was more concerned that they might be coming on TOO much, with every little slowdown, and not much annoys me more as a driver than following behind a brake tapper.

In my Toyota the cruise is on the wheel, there's no stalk

 

[eNate]

In my Toyota the cruise is on the wheel, there's no stalk

Ah, so you made me look! On the RAV4 forum a poster there makes it sound similar to the i3: press and hold the On/Off button for a few seconds and it disables distance following mode. (On the i3 it's press and hold the distance following button.)

 

[drcarrera]

As for the OP, if you were doing 30mph and the driver behind almost rear-ended you they were either going too fast or driving too close (and probably both!).

 

[ksnax]

Brake light responsiveness to regen can be set to different levels via coding. I believe it is set to the middle of 3 settings for the US market. (I changed mine at one point, and can't remember what it was before or what I set it to . . LOL)

 

[808Pants]

so I taped an inspection mirror to the back window to monitor the 3rd brake light in an attempt to understand the behavior.

I was about to ask...my guess was a selfie-stick on a modified trailer-hitch, with a smartphone set up to Facetime you on another phone...

In the early eighties I remember being amused by a Cadillac that had fiberoptic bundles set up to give dashboard indications of various light status, but in hindsight, it wasn't ENTIRELY from the Rube Goldberg school of auto engineering.