# TACC (aka adaptive cruise cntrl) is herky-jerky (not smooth)



## scottf200 (Sep 21, 2017)

I just did a 250 mile trip today on a mixture of rural roads, major highways, and 25K 'city' driving.

I did notice that the 'adaptive cruise control' (TACC) aspect of following a car seems a little herky-jerky (or speed up, down, up, down) compared to the car I'm following.

ScanMyTesla data on my '17 X 100D. Obviously speed changed some but the purple HP line gives you and idea that it wasn't smooth and you could feel it.

Others seeing this. Not sure if it is related to 2019.40.1.2 or not.

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Graphic below 2 of 2


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## TomT (Apr 1, 2019)

It seems quite smooth on my 3 with 2019.40.2.1...


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## scottf200 (Sep 21, 2017)

TomT said:


> It seems quite smooth on my 3 with 2019.40.2.1...


Just to be clear ... is that while you are following someone at the 'units' distance set?
If I'm on open road then it is very smooth still.


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## jdcollins5 (Oct 31, 2018)

On 42.1 and my car is also smooth when using a TACC and following someone at follow setting.


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## TomT (Apr 1, 2019)

Yep. Depending on traffic, I usually use from 1 to 3...



scottf200 said:


> Just to be clear ... is that while you are following someone at the 'units' distance set?


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## Grey3 (Sep 26, 2019)

My 2019 model3 with 2019.4.2.1 is also very jerky on TACC when in a traffic jam, while using 4 - 7 following distances. The constant accelerations and slow downs are giving me motion sickness. This is notable in both “standard” and “low” regen settings. I’ve also tried “chill” mode to temper acceleration without success. The car does amazingly well when the traffic is minimal with stable speed. I’m hoping that someone in Tesla is working on a “smooth ride” mode. Otherwise, full FSD feature will need to come with barf bags.


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## Feathermerchant (Sep 17, 2018)

When I had my 30 day free Autopilot trial, I found that when following people who cannot hold a steady speed, I got results like above. When I followed a steady driver (like a truck) it worked great. 
I too felt motion sickness when the car in front was pedaling.


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## Dogwhistle (Jul 2, 2017)

As a previous early access tester, I’ve complained to Tesla for quite some time about the high rate of jerk applied by TACC in maintaining it’s station keeping. It’s just way to aggressive with acceleration onset rates, when more smoothness would be much more comfortable. The amount of accel/decel it applies is mostly fine, it’s the abruptness of how quickly it applies it when not necessary that is the problem. Hasn’t seemed to change much with the latest update.


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## bsunny (Oct 8, 2018)

I noticed the jerkiness while following someone using TACC. It seems to be something, in my observation FWIW, that got much worse in 40.2 (which is what I have installed now.) It’s not jerky all the time, though, and I’m sorry to say I did not take note of under what conditions it happens.


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## jdcollins5 (Oct 31, 2018)

bsunny said:


> I noticed the jerkiness while following someone using TACC. It seems to be something, in my observation FWIW, that got much worse in 40.2 (which is what I have installed now.) It's not jerky all the time, though, and I'm sorry to say I did not take note of under what conditions it happens.


My observation has been that it depends on whether the car you are following is using cruise or not. If they are using cruise, how well is the other car's cruise working. Whenever I have noticed my car changing speed I have noticed that the lead car is changing speed. I can change lanes to follow another car and my car is smooth again.

In my experience, even after 40.2.1, TACC does an excellent job of controlling distance between you and the car you are following. The latest updates have increased the aggressiveness in following so any change in speed of the lead car will be magnified.

Have you ever followed a manual transmission car? . Every time it shifts gears it feels like my car is shifting gears.


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## msjulie (Feb 6, 2018)

jdcollins5 said:


> Have you ever followed a manual transmission car? . Every time it shifts gears it feels like my car is shifting gears.


I suppose that depends on the driver  Not me..

I am wondering if the erratic speed changes are related to the new software that adjusts your speed based what you are passing... least I feel the car has gotten worse with that change...


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## Mike (Apr 4, 2016)

I have always found using TACC, in a non freeway but rural setting, is far too jerky for passenger comfort.

I'm able to manually follow traffic that is not maintaining a smooth speed with a smooth, fluid method (based on 4.5 decades of driving experience).

Like earlier versions of NOA sticking to the center of a lane regardless of all circumstances, TACC is sticking to its following distance in the same "crude" manner.

My expectations of a mature version of TACC will include a built in elasticity of my selected follow distance to allow no more than about (I can't recall the exact figure) 0.13 g (assuming no safety issues that need to be addressed at the moment).

Right now TACC is still "ones and zeros" in its approach to station keeping behind a target.


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## scottf200 (Sep 21, 2017)

Grey3 said:


> My 2019 model3 with 2019.4.2.1 is also very jerky on TACC when in a traffic jam, while using 4 - 7 following distances. The constant accelerations and slow downs are giving me motion sickness. This is notable in both "standard" and "low" regen settings. I've also tried "chill" mode to temper acceleration without success. The car does amazingly well when the traffic is minimal with stable speed. I'm hoping that someone in Tesla is working on a "smooth ride" mode. Otherwise, full FSD feature will need to come with barf bags.





Dogwhistle said:


> As a previous early access tester, I've complained to Tesla for quite some time about the high rate of jerk applied by TACC in maintaining it's station keeping. It's just way to aggressive with acceleration onset rates, when more smoothness would be much more comfortable. The amount of accel/decel it applies is mostly fine, it's the abruptness of how quickly it applies it when not necessary that is the problem. Hasn't seemed to change much with the latest update.





bsunny said:


> I noticed the jerkiness while following someone using TACC. It seems to be something, in my observation FWIW, that got much worse in 40.2 (which is what I have installed now.) It's not jerky all the time, though, and I'm sorry to say I did not take note of under what conditions it happens.





jdcollins5 said:


> My observation has been that it depends on whether the car you are following is using cruise or not. If they are using cruise, how well is the other car's cruise working. Whenever I have noticed my car changing speed I have noticed that the lead car is changing speed. I can change lanes to follow another car and my car is smooth again. In my experience, even after 40.2.1, TACC does an excellent job of controlling distance between you and the car you are following. The latest updates have increased the aggressiveness in following so any change in speed of the lead car will be magnified.





Mike said:


> I have always found using TACC, in a non freeway but rural setting, is far too jerky for passenger comfort.
> I'm able to manually follow traffic that is not maintaining a smooth speed with a smooth, fluid method (based on 4.5 decades of driving experience).
> Like earlier versions of NOA sticking to the center of a lane regardless of all circumstances, TACC is sticking to its following distance in the same "crude" manner.
> My expectations of a mature version of TACC will include a built in elasticity of my selected follow distance to allow no more than about (I can't recall the exact figure) 0.13 g (assuming no safety issues that need to be addressed at the moment).
> Right now TACC is still "ones and zeros" in its approach to station keeping behind a target.


1) Great points and observations folks.
1a) I think there are some good points that 40.2.1 seems more aggressive/tighter on following. I have over 43k on my '17 and use AP a *lot* (bought it with 4K). 2/3rd of those miles are highway AP roadtrips. Had 38K on my '16 X. It is more noticable to me now.
1b) I think following someone on a steady cruise is reasonable smooth and seems close to just an open road with my Tesla's cruise control set. Assumes their cruise is well designed (see my 2 point below). My first post had two graphs which represented uncontrolled testing and my speed changed +/- 5mph (vs +/-1 mph in my controlled test (2)).
1c) I really liked the term "elasticity" and failing a more fluid following method. It really seems obvious that the 'calm mode' should have an impact here but it doesn't appear the let that influence AP/TACC only manual driving it seems.

2) I did some controlled testing following my wife. She was driving her Volt while on the battery and was using cruise control. She would tell me when she hit our test speed then I'd wait a few second for things to settle and I would record in ScanMyTesla for 30ish seconds.

2a) My test were done at 40mph, 45, 60, and 65. Using 5 units for the following distance. See TITLEs for mph.
2b) Roughly 100 samples / second for each of the data lines.
2c) I added front and rear torque as the combined HP line seemed to 'smooth' out the data points and I wanted everyone to see more details.
2d) It seems that 60 and 65 mph front and rear torque lines are smoother but I think the scale due to 60&65 being larger numbers 'smoothed' it out visually.
2e) I then picked 17ish seconds out of the 30ish seconds to find the smoothes/most_consistent (flat) speed for the graphs below.


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## sduck (Nov 23, 2017)

Does this "jerkiness" smooth out if you use higher follow distance setting? That used to be the cure-all for smoothing out TACC - set it to 3-4 lengths or higher and the ride would get significantly smoother. 

One thing I (and others) have been bugging tesla to improve is the follow distance at the 1 car setting - for a while maybe a year ago it was really following close, at actually 1 car distance, but at some point they broke that, and it started following too far away at the 1 car distance. So I'm glad they've tightened it back up, but doing so would require the kind of herky jerkies you're complaining about.


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## scottf200 (Sep 21, 2017)

sduck said:


> Does this "jerkiness" smooth out if you use higher follow distance setting? That used to be the cure-all for smoothing out TACC - set it to 3-4 lengths or higher and the ride would get significantly smoother.
> 
> One thing I (and others) have been bugging tesla to improve is the follow distance at the 1 car setting - for a while maybe a year ago it was really following close, at actually 1 car distance, but at some point they broke that, and it started following too far away at the 1 car distance. So I'm glad they've tightened it back up, but doing so would require the kind of herky jerkies you're complaining about.


Excellent point and question. 
5: In my testing above I was using a following unit of 5. 
I generally use 7 on the highway in modest traffic so I have more time to react if the system provides a fast red steering wheel warning (note my hands are always on the wheel).
I generally use 5 for suburb driving 35-55 speed roads
I generally use 3 for bumper-to-bumper (stop-n-go).


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## sduck (Nov 23, 2017)

Oh I see - I missed that. Sorry. Yes, if it's changed at that setting, it's definitely worth bugging tesla about.


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## scottf200 (Sep 21, 2017)

sduck said:


> Oh I see - I missed that. Sorry. Yes, if it's changed at that setting, it's definitely worth bugging tesla about.


My bad for not being clear. You didn't miss it. I didn't originally have it in there. I added it based on your feedback. Thanks.


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## Mr. Spacely (Feb 28, 2019)

Just got back from a weekend trip from St. Petersburg to Orlando and back-- about 200 miles. I used NOAP almost exclusively and was impressed. There was very little "jerkiness" and I use a pretty aggressive 2 car length setting. But the most impressive thing now is its ability to change lanes more quickly and confidently. This car is sneaking up on true self driving. Add in some stop sign and stop light recognition by year end and we are close to "feature complete."


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## Needsdecaf (Dec 27, 2018)

I have definitely noticed many instances of the car accelerating jerkily. It's not consistent, and it's not in any one situation. I've gotten it while following at a constant speed, but mostly when accelerating while traffic is starting to speed up.

Take a look at this video that I took back in october (at least two softwares ago). This is on a highway, accelerating up to full speed as traffic in front cleared. I had the car set to 72 and we all slowed down for some unknown reason, then started to speed back up. Take a look at how jagged the black power line is over most of the acceleration. It is constantly jumping back and forth, and I could feel it. Note, I was pretty far behind the car in front of me when this took place.


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## HansT (Dec 31, 2019)

It was never as good as a human driver, but mylatest update (2019.40.2.1) seems to have regressed - either that or there's actually something wrong... Now, when I engage TACC in traffic - freeway/highway or local roads - the car behaves as if it has a tremor, constantly adjusting its speed, suddenly slowing or accelerating, just generally really *jittery*. It's maddening. I've stopped using TACC because of this. Should I pull the trigger and go in for service or is this just something I have to live with?


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## FRC (Aug 4, 2018)

HansT said:


> It was never as good as a human driver, but mylatest update (2019.40.2.1) seems to have regressed - either that or there's actually something wrong... Now, when I engage TACC in traffic - freeway/highway or local roads - the car behaves as if it has a tremor, constantly adjusting its speed, suddenly slowing or accelerating, just generally really *jittery*. It's maddening. I've stopped using TACC because of this. Should I pull the trigger and go in for service or is this just something I have to live with?


I'm not sure what service might or might not do for you, but I can tell you that my TACC experience is NOTHING like you describe. Mine is consistent, smooth, and reliable. It is one of the most pleasurable features of my car. I wish and hope the same experience for you.


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## Mike (Apr 4, 2016)

HansT said:


> It was never as good as a human driver, but mylatest update (2019.40.2.1) seems to have regressed - either that or there's actually something wrong... Now, when I engage TACC in traffic - freeway/highway or local roads - the car behaves as if it has a tremor, constantly adjusting its speed, suddenly slowing or accelerating, just generally really *jittery*. It's maddening. I've stopped using TACC because of this. Should I pull the trigger and go in for service or is this just something I have to live with?


Welcome aboard!

IMO anything to do with autopilot/TACC has regressed since we got V10.x.

But in your case, if it is always "jittery", I'd call it in for a closer look.


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## scottf200 (Sep 21, 2017)

HansT said:


> It was never as good as a human driver, but mylatest update (2019.40.2.1) seems to have regressed - either that or there's actually something wrong... Now, when I engage TACC in traffic - freeway/highway or local roads - the car behaves as if it has a tremor, constantly adjusting its speed, suddenly slowing or accelerating, just generally really *jittery*. It's maddening. I've stopped using TACC because of this. Should I pull the trigger and go in for service or is this just something I have to live with?


I'd probably wait until the latest round of 2019.40.50.x bug fix updates get stabilized and you obtain it.

I sure wish they'd let the 'calm mode' have an impact on TACC (follow) & AutoSteer/AP (centering). I'm sure there is a reason but it seems like they could take 10% off or something of the normal acceleration at least. I'm thinking slower elasticity here.


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