Regen braking tail lights

Regen braking tail lights

Do the brake lights come on when slowing down using Regen braking? How do the cars behind you know you are quickly slowing down if the brake lights don't come on?

Volker.Berlin | 23 oktober 2012
STEVEZ | 23 oktober 2012

Yes, the brake lights come on during regen, just like the Roadster's did. It's a software response tied to accelerometers: the brake lights come on when the car decelerates, whether you push on the brake pedal or not.

Michael23 | 23 oktober 2012

They come in a lot. Drivers will think you love to brake, but then you'll leave them in the dust.

Brian H | 23 oktober 2012

To get the most from playing with the minds of tailgaters, lift foot from the goose pedal for a few seconds, then floor it!

jbunn | 23 oktober 2012


Yep. I got totaled July before last. Was in the decel lane on an exit and got plowed into at highway speed by a young girl borrowing her parents SUV to move.

Bought the truck back from the yard and still driving it (replacing the car at that time was not part of my Tesla master plan). Spent a lovley July Friday in an MRI machine and was treated for a concussion at the ER.

Next Friday, same exact spot. Light rain, 60 mph, Masarati 20 feet off my smashed in back end. I don't understand some people.

But I'll do the same thing. In an ice, you mash the brake and gas at the same time for an instant, then release the brake. You car appears to halt, then disappear from the space they just plowed through. Serves them right if they have to change trousers. What if it was a deer, or a dog, or a kid? Can they stop? Would they plow into me and cause me to run over the kid anyway?

Other than that, I try to ignore it. I just tip the rear mirror up, and out of sight out of mind. I lock the speedo just above the limit, and I'm not willing to get a ticket for some asshat. So, if they are behind, sucks to be them.

We used to have a line you could call for agressive driving. Closed due to budget. Would really like to have that line open once I get a rear camera....

jbunn | 23 oktober 2012


Wanted to get a sticker for the back that said "The last tailgater made my Tesla downpayment", but I don't have much of a bumper left for a sticker.

Timo | 23 oktober 2012

I wonder if the brake lights lite up a bit too soon. In a video I saw about Model S it looked like they did light up before you actually regen, when speed was slowing just by lifting your feet a bit from the accelerator. They also "flicker" meaning that there is no threshold between light on lights off. I mean if you are just at the borderline of brake lights going on, you should be able to get "a bit less deceleration" before lights go off again.

I think brake lights should come up only when you actually hit the deceleration that is greater than coasting IE. you actually regen brake, not just slow down.

----------> deceleration increases
lights off lights on
actual regen.

Timo | 23 oktober 2012

d*mn. Lets try this with pre and H6

----------> deceleration increases

lights off lights on
actual regen.

Volker.Berlin | 24 oktober 2012

Timo, with a due respect, I think it is extremely hard to judge these kinds of things from video, and until we have first hand experience, any debate or critique is pointless. Tesla has shown that they are not technologically naive, and I'm sure they have heard of a hysteresis before.

Timo | 24 oktober 2012

I obviously don't have any experience about Model S, but in the video I saw the lights "flicker", which means that either there is no "hysteresis" or that driver in front of the chase car had really restless accelerator foot. Or did rest his/her other foot onto brake pedal. Pressing that should obviously light up brake lights immediately. Anyway, it looked weird.

Volker.Berlin | 24 oktober 2012

Or it's a video artifact because the frame rate of the video interferes with some properties of the light source. Do you really believe that the wheels slowly turn backwards when it looks like it on video?

Volker.Berlin | 24 oktober 2012

Some newer cars have two stages of brake lights: The regular brake lights that come on during normal driving, and some kind of "super brake light" that indicates really hard braking. On a BMW, e.g., the "super brake light" quickly pulses to unmistakably warn drivers behind the car. I haven't heard of it but I wouldn't be surprised if Tesla had a similar feature. Maybe that's what you saw?

Timo | 24 oktober 2012

It wasn't steady flicker, and when the car actually brake lights were solid. If it were a video artifact then those lights should have flickered then too.

OTOH it could have been "prototype -issue", because IIRC it didn't light up entire back light area either, only the area that is in "bumper" not in the boot, and (again IIRC) people here have said that final product does light up entire back of the lights. It was video of one of those early "get amped" test drives if I remember correctly.

Vawlkus | 24 oktober 2012

This should answer your question Timo: what is the trigger for the brake lights? I remember reading (although I forget where exactly) that the brake lights aren't triggered by regen kicking in, but by the cars accelerometers indicating deceleration. Depending on the components and levels used, there could be a 'neutral' speed that could trigger a flickering of the brake lights as you describe.

Brian H | 24 oktober 2012

I'd actually prefer amber for regen, red for actual braking.

Volker.Berlin | 24 oktober 2012

Brian H, I don't see any of your notorious smileys. You must be kidding.

sagebrushnw | 24 oktober 2012

@ Brian H

Agree on the Amber for regen, red for actual braking, or maybe when the brake pedal is applied, a rapid flashing of the red brake lights and then steady.

Teoatawki | 24 oktober 2012

No car has amber brake lights at this time, so this will confuse drivers. Not a good plan.

Amber is only approved for turn signals, (required in EU) and I really wish TM had adopted amber turn signals worldwide, rather than red for the US.

The 'super brake lights' feature is not currently approved in the US. A test program allowed 5000 BMWs equipped with the 'super break lights' to be sold in the US. Perhaps the feature will soon be a recommendation if it proves to be effective. Personally, it seems like it has to be.

Volker.Berlin | 25 oktober 2012

Teoatawki, thanks, that's interesting. I see them increasingly frequently around here in Germany. Naturally, they usually only come to use on the Autobahn, not around town, where speed usually is low enough not to trigger them even when stomping on the brakes. Going from 20 or even 30 mph to a stop usually isn't too dangerous, even when stopping suddenly.

It's a different story when coming down from 110 mph or more to 50 mph or less (e.g., due to a slow vehicle changing lanes, or a bottle neck), when there's someone behind you going at the same speed. It makes a huge difference at that speed, if the car in front just touches the brakes or strongly decelerates -- but without the "super brake lights" (my term, sorry, don't know any better) it often is extremely hard to tell the difference from behind -- your view may be obstructed by the terrain, or by the very car in front of you, so that it is impossible to tell the reason for the other car braking, even if you pay attention.

Bottom line: I think there's a huge pro, and I can't think of any cons. However, I also think they are most useful (and actually needed) at "stupid" German autobahn speeds. At speeds up to 80 mph, most vehicles go at approximately the same speed and these dangerous situations rarely happen at all. Which is one argument for a speed limit on German autobahns, but that's a different discussion... ;-)

sagebrushnw | 25 oktober 2012

@ Teoatawki

"No car has amber brake lights at this time, so this will confuse drivers."

Yes, no amber brake lights but some metro buses have flashing amber (like your hazard/four way lights) or alternating amber lights to get your attention that they are slowing down, not accelerating.

DavidG | 25 oktober 2012

Automatic brake lights were implemented in the early 1900's. Yes that early. The problem was that those incandescent tail lights were lighting up when parked in the garage. Result was a dead battery and an unhappy customer. As batteries were really expensive then, a federal law was passed that said the brake lights may only come on when the brake pedal is depressed.

100 years later, computer control and accelerometer sensor capabilities have improved. But has that law been rescinded, or is it just being ignored? ;) I'm OK either way.

jerry3 | 3 november 2012


It's still enforced in Europe.