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A heads up: Brake lights when coasting

I was on the freeway today and a motorcycle was tailgating me. I let off the accelerator while glancing in the rear-view, and this triggered my brake lights, so the guy thought I was messing with him, and passed while making a gesture. Now, I don't know why he didn't just lane split to begin with, it's legal here, but it serves as a caution: the Tesla lights it's brake lights every time you release the accelerator pedal and the car begins to regen/decelerate, and some could misinterpret this as an intentional braking action.

If the car is slowing down, why wouldn't you want the brake lights on? Yes, in a manual you could use engine braking to slow down without alerting the tailgater and have him run into you, but it seems like you would prefer to avoid that.

And it's not every tine you let off the accelerator; it's when the accelerometer determines that you're slowing down as much as if you were actually braking.

In my car, it is exactly at -30kW regen.

Nevertheless, for new owners it is important information. You need to adjust your driving style to single pedal driving. If you want to coast, don't take your foot completely of the accelerator but keep it pressed to adjust your speed. (It's not really "coasting", I know.)

And, obviously, you did read the manual, right? ;-)

"NOTE: If regenerative braking is aggressively
slowing Model S, such as on a steep descent,
brake lights turn on to alert other road users
that you are slowing down."

I admit that this text is not very clear (why do they mention the steep descent?), but it is a direct copy paste from the manual.

I actually don't see the issue, other than that you were tailgated by an a-hole on a motorcycle. And that's his problem.

@mrspaghettii I agree. Some people seem to find it uncomfortable when their intentions are misunderstood . . . even when they are misunderstood by a jerk.

I believe in some areas "break checking" or tapping your brakes in response to someone tailgating you could get you fined for aggressive driving (not to mention cause an escalated response/road rage situation).

On the 17" console, running SW version 4.5, press the Tesla "T" at the top to bring up the release notes screen. The car on this screen is animated and you can see when the break lights are on. My MS turns the break lights on at 15 KWh regen.

@DFibRL8R, Really? I have never heard this but it would not surprise me to find it is true.

I have read accounts of drivers who brake check getting cited or found at fault in accidents. That said, I would think there's a difference between slamming on the brakes and the gentle deceleration when you let of the accelerator in the model S. I suppose a tailgater could over-react and run off the road but the bigger issue is inciting road rage.

I would hope the person tailgating would be pulled over for not following at a safe distance before ssomeone sowing down. If you let off your accelerator enogh for regenerative braking to begin the brake light should come on longer than just appearing to be a brake check.

I believe in some areas "break checking" or tapping your brakes in response to someone tailgating you could get you fined for aggressive driving

How is this enforced? Is there a statey that can see that the car in back of you is tailgating and doing nothing about it? How can the statey see that you're brake tapping if he's not behind you? Is he the one tailgating? If not, can he see through the car that's tailgating?

There is no brake light when using the LOW setting in regen. The MS will act just like an ICE vehicle. The STANDARD setting in regen you will have brake lights once you feel your body going forward. The kW reading on regen does not really matter. It all depends on how much you let your foot off the pedal.

Press the battery icon on the top left will give you a large picture of you car, then you will see the brake lights on or off.

This could have gotten me in trouble this morning.

Driving in to Texas Medical Center through a residential neighborhood well known for aggressive policing (South Side Place for Houstonians), I was first at a red light. I took off pretty fast, but not all the way down, and I got to only a few miles over the 35 MPH limit. I didn't see where he came from, but a couple of blocks later a police car came up very fast (well over the limit) and tailgated me aggressively. No lights, but he was definitely within 5 feet at times. I obviously maintained a safe and steady pace, and he left after a few blocks (ridiculously small jurisdiction for this micro town). Clearly harassment. Very glad a misinterpreted regen brake light didn't make it worse.

Guys, there is no issue or difference here - the brake lights come on when the car slows down. Just like any other car.

@shop - agree 100%. There have been many other threads on this, but it works exactly as it should. And the Tesla icon animation thing can answer any questions.

I have a slight disagreement on the 'no issue' comment.

On an interstate, ICE cars slow down due to coasting. TMS slows down with brake lights, (with a slight margin, say 15 kw regen) which could be interpreted as brake checking. I have done some investigation about when the lights turn on during what is 'light' slowdown on interstate roads. There does seem to be that thing where you coasted and thought lights weren't on, but thy had come on. May be the software can factor in current speed as well when deciding to tun them on? Increase the margin at anything above 65 and keep it normal below that?

On street roads this is no issue, however.

@Theresa He is right about brake checking. Same as flashing headlight to signal slower moving cars on the fast lane you want to go faster can be looked at as aggressive and provocative behavior and be ticketed in California even though it's a standard practice on European highways. All these are not bad as tailgating of course.

I would estimate 75% of drivers follow way to close and "tail gate". I do not. I allow plenty of braking distance at any speed...and more on the highway. I also use the "low" regen in the Model S.

The majority of drivers have no concept that they following to close. The things that make you say hmmmmmmm...

Edit: That they ARE following to close.

Brake lights turn on based on accelerometers, so that is equivalent to regen torque, but not power. Therefore, regen power to activate brake lights depends on speed.

In standard regen mode, when you let your foot off the accelerator the car slows much faster than if it were coasting. If you want to be able to coast in Model S without brake lights coming on when you release the accelerator, switch to low regen mode and your "issue" is solved. It will behave just like an ICE vehicle.

However, having brake lights come in standard regen mode is absolutely appropriate due to the heavy slowing exhibited by the car. In Model S, standard regen slows the vehicle at the same rate as if you applied braking force in an ICE vehicle. It is NOT like coasting! When you slow down at such a high rate, then the brake lights must come on because they would in any other car when your forward acceleration slows at such a rapid pace.


"On the 17" console, running SW version 4.5, press the Tesla "T" at the top to bring up the release notes screen"

This feature no longer exists in 5.0. I think it is really useful for new owners so I'm sad to see it go.
But once you get used the car, you don't really need it.

This isn't "brake checking" i.e. tapping the brake pedal for the sake of triggering the brake lights. The regen is actually slowing down the car. The lights only illuminate in response to the deceleration. This is a much more logical way to apply the brake lights than the way it is implemented in most ICE cars.

Well, I disagree on 'non-issue' - here's what happened on 4th of July.

I was driving home after watching fireworks (about 10PM) and suddenly a police car followed me and made me stop. After some chat and checking 'who is who' he said that I was driving 'erratically' as the reason for pulling me over. I didn't get his explanation at the time, but some weeks later I did notice brake lights coming on when I was cruising! I was my first month back in July and I had no idea why police car was following me, but after reading this thread I think some people just don't get the 'new driving style' of an electric car.

I have to be more careful with driving after sunset on my S60 just to not waste time for chats like this !

As folks have noted, the system works the way the system should; when you have regen set on the standard level, the auto slows quite a bit, and the lights come on, as they should.

My only point was to give folks a heads up: your tail lights are doing a lot of blinking you may be unaware of, and this may confuse other drivers, the police, etc. Don't be surprised if you get some reaction, along the lines of "why the heck is that guy in front of me braking now??", etc.


I did some testing today and determined the lights come on at a particular accelerator pedal angle and not at a specific regen level.

For example, when going about 15 mph, the lights came on at about 5kW while at 40 mph, about 30kW with Inbetween speeds giving inbetween power. All at seemingly the same pedal angle.

skymaster | August 29, 2013 new
Edit: That they ARE following to close.

Edit Edit: That they ARE following TOO close.


I'm not brake checking. It's because I thought a cat was going to run in front of the car, saw a deer in the woods, a piece of debris in the road, or someone in front of me slowing down.

If you rear end me because you are tailgating it's your damn fault, and you're paying for back massages for the next year.

It's the responsibility of the person behind me to keep their distance, and be able to stop in a controlled manner.

+100 @ jbunn, couldn't agree more.

The solution to avoiding erratic flashing of brake lights is to not completely let off the pedal in your Model S when you want to slow down. Instead, gently ease off the pedal and control your slowing using just the one pedal. If your body lurches forward, you've let off the pedal too much, so next time ease up less. Once you get the hang of it, your gentler foot motion will lead to more consistent and sensible brake light behavior to those behind you. If you want something close to "coasting", gently ease off on the accelerator until your regen and energy usage are both as close to zero as possible. This will allow for simulated coasting without activating your brake lights.

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