Brake lights

Brake lights

Driving home today, the regen slowed me so successfully I worried I might be rear ended. Does anyone know if the brake lights go on even if you don't press the brake?

agiangone | 12. helmikuu 2013


kublai | 12. helmikuu 2013

At night, drive with your rearview cam on and you'll see the brake lights come on when you let off the accelerator.

tguy600 | 12. helmikuu 2013

thanks for the pointer kublai.

jbherman | 12. helmikuu 2013

If you press the Tesla "T" icon top center of your display, it will show you when the lights go on and off...brakes included.

exPGAhacker | 21. helmikuu 2013

Shouldn't this regen brake light be adjusted for certain speed levels? My fiancee was behind me the other night and she was kidding me about riding the brakes. At some speeds, letting off the accelerator shouldn't automatically trigger the brake lights... IMHO.

olanmills | 21. helmikuu 2013

@billberndt The brake lights come on based on accelerometer, so they come on whenever the rate of deceleration exceeds a certain measure.

There are two exceptions to this rule:
-The brake lights come on whenever you physically press the brake pedal
-The brake lights come on if you are not pressing either pedal at all and regen is at full strength (kW guage showing -120 kW)*

*I've noticed that in this scenario, even if the car is holding a steady speed, the break lights come on. This scenario can happen when you're going down a steep hill at a high speed (60 mph).

Carefree | 21. helmikuu 2013

I must say that I am not too thrilled about the regen breaklights coming on most of the time. I always hate to drive behind someone with a "nervous foot" - breaking all the time. All us Tesla drivers will be one of those nervous drivers now. I fully understand why this needed to be implemented by Tesla but I don't like it:-)

olanmills | 21. helmikuu 2013

I really don't get what the concern is. They don't come on unless the regen is slowing you down to the point that it's similar to braking with the disc brakes.

If you are worried about the brake lights coming off and all the time, well then don't drive that way.

ian | 21. helmikuu 2013

Do they come on if you dial the regen back to the lighter setting? Or is it all based on the amount of deceleration no matter what?


gregv64 | 21. helmikuu 2013

@ Carefree: (olanmills +1) If you are constantly doing regen and then accelerate rather than using a constant amount of power you are wasting some amount of energy and are exactly the "nervous foot" type of driver you dislike. You use regen when you want to slow down, just like you used to use the brake pedal. If you're cruising on the freeway your brake lights should not be coming on. (Note that a small amount of regen while slowly decreasing speed will not cause the brake lights to come on.)

Superliner | 21. helmikuu 2013

Brake lights coming on, upon vehicle deceleration via regen "I believe" (not 100% sure) is required by law. And if it is not "It Should Be".

Would you rather be rear ended because no one knew you were slowing or put up with the brake lights on your car which you can't see anyway "unless using your display or rear view cam" both of which are not advisable when underway more than necessary.

Brian H | 22. helmikuu 2013

If a putt-putt is heading down a steep hill at 60 mph, don't you think the brake lights would be on as the driver burns up his brakes? What's the problem?
And give the breaks a break, OK? It's brakes.

jemartin | 23. helmikuu 2013

I agree with err-on-the-cautious side comments above, but I still think that the brake lights come on too soon at high speed. I'm sure it makes people behind nervous and could potentially cause massive slow downs, behind, when too many Model S are on the road :-)

Seriously, I still can't figure out how the lights are controlled. I thought they came out at or over 20KW of regen, but that's not the case at low speed. Some have suggested they're controlled by an accelerometer, but that doesn't seem to be true at high speed. Plus, why would you use an accelerometer when you have access to real time speed readings and can derive deceleration from it...

And the best way to see the brake lights in action is at night using the rearview camera, when nobody else is around. I wouldn't use the screen that pops up when you press on the "T". It's too distracting if you also want to pay attention to what's happening in front of you.

TikiMan | 23. helmikuu 2013

I actually like the fact that my break-lights going off more than normal might annoy drivers behind me, because there is more a chance someone who likes to rubberneck, will just switch lanes, thus there is far less of a chance of getting rear-ended.

I have been noticing this a fair bit more while driving in the HOV lane. I hate rubberneckers (aka tailgaters), and the MS is not a car they enjoy doing their hobby behind ;-)

Getting Amped Again | 23. helmikuu 2013

I feel safer in my S because I leave more room in front of me to ensure I have room for a regen-only slowdown, and I think other drivers leave more room behind me because they see my brake lights come on often. It's like I have a force field around me!

Andre-nl | 23. helmikuu 2013

"Plus, why would you use an accelerometer when you have access to real time speed readings and can derive deceleration from it..."

That method doesn't work when going downhill when you have to brake to just to keep the same speed. People expect the brake lights to come on in that situation, but your method then doesn't work because it detects a constant speed.

olanmills | 23. helmikuu 2013

@Andre-nl just because people expect brake lights to come on when going down hill even if you are actually increasing speed does not mean they should come on. It gives no useful information to the driver behind you. Since brake lights do not indicate the intensity of the braking, brake lights when going downhill with ICE actually can mask your actions a bit, and reduce the raction time of someone behind you if you go from dragging the brakes to hold speed downhill to pressing them fully to slow or stop.

@je-martin and everyone else really, I still don't understand why you guys think the brake lights come on often. Check the car's display when you press the 'T' icon (it shows the status of the car's brake lights). You will notice that the brake lights only come on when the rate at which you are slowing is similar to the effect of pressing the brake pedal in an ICE. They do not come on too often.

If they are coming on often for you, it means that you are pressing down and letting up on the accelerator too much and too often. In an ICE car, this would be like constantly hitting the brake pedal whenever you want to slow down at all, rather than easing of the accelerator some to slow more gradually.

The brake lights work perfectly as is. Learn how to control the car with just the accelerator.

Brian H | 23. helmikuu 2013

I was speculating what one could do with "break" lights. After a crash, they come on? ;p

Roblab | 23. helmikuu 2013

My wife, following behind, says brake lights do not go on when I am in Low Regen mode. The regen is gentle enough that the accelerometer does not activate.

You are still able to slow, but with less aggressiveness. If you allow room and slow with regen and no brakes, you do not lose any of your regen power, you just have to plan ahead and keep more distance. Or use the brakes.

Andre-nl | 24. helmikuu 2013

@olanmills Safe driving is about predicting the future a few seconds ahead. I would say expectations are everything. Just my 2c.

Brian H | 24. helmikuu 2013

Yes, "drive to where the hole will be." (A modified hockey quote from the Great Gretzky; "Skate to where the puck will be.") | 24. helmikuu 2013

@olanmills - 120 KW/h regen? I only have a maximum of 60 KW/h regen (the limit of the display even when nothing is happening). Has anyone else noticed this difference or know what options cause it? I have a single charger, 60 KW model. Does the twin charger get you 120 KW/h regen or is it a 85 KW model?

I can't say I miss it (never having it), as the regen works great.

If twin charger gets you 120 KW/h regen, I wonder if it improves the system efficiency. I guess only Tesla would have the numbers, but if it does improve the system efficiency, it might be a reason to get the twin chargers.

nickjhowe | 24. helmikuu 2013

@Frank2 - Does the inverter even play a role when not charging? The car can put 320KW into the motor (per the display) but only 60KW on regen (on my P85, single inverter)

olanmills | 25. helmikuu 2013

@Frank2, the increments seem to increase exponentionally, every major tick is double the value of the last.

The -60 kW tick is not at the end of the guage, so I assume that the very end, which is not marked, is -120 kW.

Sorry if that caused any confusion. I do have the twin chargers, but I think the guage display looks the same for everyone.

mal42north | 25. helmikuu 2013

When going down a steep hill at constant speed, the brake lights will come on if you are using sufficient regen to keep speed. Even though you are not changing velocity, part of the acceleration due to gravity will be acting in your forward direction. Assuming Einstein was right this is indistinguishable from actual acceleration (deceleration in this case).

Brian H | 25. helmikuu 2013

You are continuously changing velocity from free-fall. Partly the road pushing up, partly the resistance of the wheels to "free-wheeling" (supplied by the drive-train and/or brakes). Just don't continuously try to figger "which leg comes after which"; you'll end up flipped, in the ditch. :D

pchapes | 09. maaliskuu 2013

Always wondered why cars don't have yellow lights for when you lift off the gas (battery.)

TikiMan | 09. maaliskuu 2013


Because, most folks speed up when they see a solid yellow-light ;-) | 09. maaliskuu 2013

@olanmills - Thanks for the clarification about 120 KW regen marker. I'm fairly sure I've never seen more the 60 KW of regen, but I'll have to try it out again and see if I can get it to go beyond the 60 KW tick.

In thinking about it more, I don't see the single/twin chargers being used for regen. These are only rated for 10 KW each, so if you have 60 KW of regen on a single charger car setup, it seems the charger would not be able to handle it.

glaserud | 09. maaliskuu 2013

The chargers aren't used for regen. This is accomplished by the inverter (now turned rectifier).

nickjhowe | 09. maaliskuu 2013

Thanks @olanmills. Will take a look. From my understanding the drive inverter is the thing that takes care of AC/DC conversion for both propulsion and regen. The single or twin chargers are only used for charging and play no part in regen.