Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

Will car speed up when not on autopilot to avoid being rear ended?

I was driving down a steep road today and went to brake at a red light before turning right. No cars in front of or beside me, roads were dry, no abrupt stop, etc. All pretty boring stuff, except...

...as I was slowing down with my foot on the brake, I could have sworn the car accelerated fairly quickly without my lifting my foot off the brake. I looked behind me and there was a car there, but nowhere close to me, although I didn't have my USB drive plugged in (it was full and I forgot to put it back in the car), so not sure if he came to a sudden stop or not (I didn't hear any brakes screeching, and nothing seemed at all out of place when I looked back).

I only mention the hill because I know it will give me a warning when I'm accelerating up that same hill and a car goes to stop/turn in front of me. I've filed a bunch of bug reports, but have given up at this point (I can't imagine the system wouldn't be able to tell that I'm on a steep hill and compensate accordingly, but, as a fix, I've adjusted the setting to warn me "late" because it will trigger nearly every day otherwise).

Anyway, I'm almost sure I wasn't imagining things today, and I only went forward a few feet, but I was wondering whether it could have been a safety feature of the car that pushed me forward? I've never felt anything like that from a car before...I thought maybe I had slipped on black ice or something, but it definitely felt like an acceleration (and it was nearly 70 degrees today). I know you hear stories of people hitting the "gas" instead of the brakes, but I was just stopping in the ordinary course and didn't move my foot once I felt it moving forward (other than to press the brake harder).

Just thought I'd post to see if I'm hallucinating.
 

ecarfan

Well-Known Member
Moderator
as I was slowing down with my foot on the brake, I could have sworn the car accelerated fairly quickly without my lifting my foot off the brake.
I understand that you are describing your perception of the experience but I don’t see how that could happen.

I'm almost sure I wasn't imagining things today, and I only went forward a few feet, but I was wondering whether it could have been a safety feature of the car that pushed me forward?
Not that I am aware of.

I thought maybe I had slipped on black ice or something
Black ice in September in Vancouver at 70 degrees?

If you had your foot on the brake and then accidentally also pressed on the accelerator pedal their would be an audible and visual alert. You do not describe any alerts, so I assume you were not pressing on both pedals simultaneously.

I can’t explain what you experienced, but I am confident that currently no Tesla sold to the public has the capability to accelerate forward if the AP sensors detect an imminent rear collision.
 
What do you have your regen set to? Sounds like regen cut due to (maybe?) tire slippage.

Interesting point! It's set to standard and I do my best (really just for "fun" as a former stick diehard) to try and avoid using my brakes (to the point of having hit a curb going around a corner trying to avoid braking--so dumb).

But driving into work today at the same spot (before seeing your post), I realized there's no possible way I inadvertently hit the go pedal. I was starting to think something might be off with the car, but if regen disengages if the ABS kicks in, I would buy that may well have been what happened. In other words, coasting to a stop with a lot of regen and a little braking. Wheels lose traction and ABS engages and regen disengages, which is why I felt a "lurch" forward and came to a stop when I gave it more brake.

I'll go with that as a working theory! Thanks!!
 
  • Like
Reactions: Phlier
Thanks guys!

If Diamond G is correct that regen disengages if ABS engages, that makes a lot of sense as to what I might have felt, and something I will think about when daily driving (particularly, as you point out ecarfan, that in Vancouver I will encounter rain WAAAAY more often than black ice, which could also trigger ABS). Again, if true, then I won't rely so much on regen where the conditions are such that the ABS could kick in with a lot of regen and a "bit" of braking (speed dependent, of course). It just didn't dawn on me that I could lose "braking (regen) power" without lifting my foot off the brake.
 
  • Like
Reactions: Phlier

KenC

Active Member
Sep 4, 2018
4,666
4,390
Maine
It sounds like what sometimes happens with blended brakes, but the Tesla doesn't have blended brakes, so the only thing I can think of is you hit a bump and the traction changed momentarily. So, presumably, you were only touching the brake pedal lightly, and most of the braking was due to regeneration, a little bump, and that would affect the regen amount.
 
Thanks Ken. I'm nearly certain something like that is what happened, but I have to confess to now being confused as to what's actually happening (and, more importantly, what I should do as we move into wetter/colder weather).

I just spotted the following post on one of the Tesla forums (Does Regenerative Braking Use Traction Control/ABS? | Tesla), but I'm not exactly sure what the upshot is. Should I be turning down the regen as we move into wetter/colder weather and relying on my brakes more? Not really following the "blended brakes" comment TBH, or the point below that the model 3 should be able to modulate the amount of regen in an ABS-like manner. I take it that regen braking does not function the same way as normal braking (re: ABS and traction control), which is why you want to tone down the regen in the winter so you don't lose the ABS and traction control functions?

Does Regenerative Braking Use Traction Control/ABS?
Submitted by Jiver on July 31, 2018

In my Volt, regenerative braking does not trigger the traction control system or ABS. Those systems are only activated if the brake peddle is pressed. This means that if I am driving in slick conditions (snow) that I have to drive in "two-peddle" mode and reduce the aggressiveness of the regenerative braking. If you do not do this, the rapid deceleration of the front wheels can cause the back end to break loose (exciting but not fun). In the same situation, if you use the brake peddle the traction control system prevents this from happening.

How does it work in the M3? In slick conditions do you need to reduce regenerative braking so that you are using the brake peddle to engage traction control or does the system engage itself such that you can stay in maximum regen mode all the time?


spuzzz123 | July 31, 2018
Haven't had it in the winter yet so no first hand knowledge. From the owners manual:

"Warning: In snowy or icy conditions Model 3 may experience traction loss
during regenerative braking, particularly when in the Standard setting and/or not
using winter tires. Tesla recommends using the Low setting"

...

Rocky_H | July 31, 2018

Yes, long time owners of the rear wheel drive Teslas have found that switching it to low regen in very slick conditions is a pretty good idea. All wheel drive wouldn't have as much of an issue, because it is able to spread out the slowing among four tires, so you can get the slowing you want with less chance of losing grip.

mscott | July 31, 2018

On my S85D, I've noticed this has gotten better in the past year. Last winter I didn't need to switch to "Low" regen when I otherwise needed to in the past. The car really should be able to modulate the amount of regen in an ABS-like manner, and maybe it does on S/X but not yet on 3?


jimglas | July 31, 2018
@Spuzz18:

thanks for that info. Makes sense.
 
Interesting point! It's set to standard and I do my best (really just for "fun" as a former stick diehard) to try and avoid using my brakes (to the point of having hit a curb going around a corner trying to avoid braking--so dumb).

But driving into work today at the same spot (before seeing your post), I realized there's no possible way I inadvertently hit the go pedal. I was starting to think something might be off with the car, but if regen disengages if the ABS kicks in, I would buy that may well have been what happened. In other words, coasting to a stop with a lot of regen and a little braking. Wheels lose traction and ABS engages and regen disengages, which is why I felt a "lurch" forward and came to a stop when I gave it more brake.

I'll go with that as a working theory! Thanks!!
This has happened to me three times. Once under slick conditions and twice under dry conditions, always while parking. Not sure I buy the regen idea but will try to replicate it based on your theory above.
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
14,274
18,406
San Diego
is correct that regen disengages

It does not even require you to be on the brake for regen to disengage. If the traction control system detects loss of traction, you can have a very quick release of regen.

I have some rough sections of pavement on a downhill every day, and if I take the worst path over the biggest bumps, the car will “surge” forward due to regen being reduced temporarily. Not on the brakes at all. Lasts just a fraction of second then it comes back.
 
  • Informative
Reactions: 9-Volt and Phlier
I have a Snow Day setting for my seat, etc., and it switches the acceleration to chill mode and regeneration to low.
Did not know that was possible. Thanks for that info.
9 - Volt: is it possible there was something to the side of the car or you got close to a curb? I have had my M3 accelerate but also give a slight forceful jerk to the steering wheel just for 1/2 second or so. I am usually a minimum 50-60CM (1-1/2' - 2') away from the curb but it might even be a pothole that causes it. Had a car turn to the right of me the other day and I got a RED vehicle and Strong Warning - can't remember the exact words though. I am still learning though.
 
Really appreciate all the responses!

Ken -- great idea to setup another driver--"SnowMan"--in the profile for snow days!

Manitoba K -- not even close to the curb this time, but thanks for bringing up the painful memory of my curb rash!!

For now, I'm going with [edited to give credit where credit is due] @diamond.g's theory, seconded by @AlanSubie4Life (loss of traction causing disengagement of regen), but, in the back of my mind, I'm a little with @BigMod3Fan--it was a dry day and I would be surprised if the tires lost traction (but MAYBE on some oil/bumps as the pavement is rough in that spot).

Will pay more attention going forward, and not be so casual about "one pedal" driving (particularly if the road conditions aren't great), now that I realize my "brakes" (regen) can cut-off for a split second if there's a loss of traction.
 
Last edited:
  • Like
Reactions: AlanSubie4Life
Just to close the loop...I had the same thing happen again tonight (but this time, less "dramatic"--although likely because I was expecting it?). Same road/spot, but this time I was paying attention. My foot wasn't on the brake (probably same as the first time). There's a little spot where the pavement sort of "drops off" a bit...nothing drastic, but it looks like enough for the regen to cut off, which then causes the "brakes" (regen) to stop working. Just thought I'd circle back, as I now don't think it was oil on the road or the tires losing traction; instead, it looks like the "bump" theory mentioned earlier in this thread is what is happening. Probably nothing particularly insightful for those in the know, but hopefully it helps someone new to the scene. Again, thanks for all the help!
 
  • Informative
Reactions: AlanSubie4Life
Really appreciate all the responses!

Ken -- great idea to setup another driver--"SnowMan"--in the profile for snow days!

Manitoba K -- not even close to the curb this time, but thanks for bringing up the painful memory of my curb rash!!

For now, I'm going with [edited to give credit where credit is due] @diamond.g's theory, seconded by @AlanSubie4Life (loss of traction causing disengagement of regen), but, in the back of my mind, I'm a little with @BigMod3Fan--it was a dry day and I would be surprised if the tires lost traction (but MAYBE on some oil/bumps as the pavement is rough in that spot).

Will pay more attention going forward, and not be so casual about "one pedal" driving (particularly if the road conditions aren't great), now that I realize my "brakes" (regen) can cut-off for a split second if there's a loss of traction.
Come to think of it, in my last "dry" incident the parking space had a raised manhole cover in the middle of it and the pavement was undulating. So, maybe there's something to the rough pavement idea. Still don't get why wheels would lose traction though, especially at such low speeds.
 

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top