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Car adjusting speed for Speed Limits ?

VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,757
6,326
Surrey, UK
Ok, nothing, nada, zilch. An hours test trip across two different counties on 'local roads' using both TACC and AP and not a single speed limit change - or a green light chime. But plenty of speed signs being recognised and stopping for red lights. On a couple of occasions, I also gave it an uncomfortable amount of time in which to respond - likewise same with green light chime.

I don't know what's going on?

On my return I double checked settings and all look correct - green light chime and stopping both enabled. Mid drive, I even adjusted my speed limit offset to +1 (from 0) on off chance that that was having an effect.

One thing I did notice (I think its been in all along but I was paying more attention this time :oops:) is that if you engage TACC and you are above displayed speed limit, then TACC speed gets set to current speed, but if below displayed speed limit, then TACC speed gets set to displayed speed limit.

But this didn't seem to make any difference to its lack of ability to set TACC to displayed speed limit.
 

Cnixon

Member
Mar 5, 2020
496
159
Basingstoke
I feel that speed limits with numbers are updated based on map data but the national speed limit signs are updated from camera. I had a 2015 model s which seemed to be camera based for all signs.
 

NorfolkMustard

Active Member
Apr 18, 2019
2,216
2,204
M3P w/FSD
Chime on green working for me too. When at the front of the queue for the lights, pulled up to them when they were already red. I’d say it was less than 2 seconds before it chimed to let me know they changed to green
 

mnobleuk

Member
Aug 2, 2019
71
74
Belfast
Wow - so many variations. My 2019 Model 3 SR+ with EAP has been consistent for a good while with a number of software updates :

1. On entering a speed limit lower than what EAP is currently set to, EAP lowers the speed to the new limit and slows the car
2. When leaving the lower speed limit, nothing happens, but if I tap the speed limit icon (red circle with the speed limit in it) EAP changes the desired speed to the new speed limit and car speeds up
 

Tony Hoyle

Active Member
May 7, 2019
1,202
743
Stockport, UK
I've had nothing at all.. I've literally driven past clear 30mph signs and the tesla insisted the speed limit remained at 40, despite showing the image of the sign so it had recognised it. It's all map data based it seems (which is often wrong) As above no green light chimes, but maybe I didn't wait long enough.. got away with 5 seconds, wasn't prepared to risk a road rage incident by trying longer.

So many diferences I wonder if Tesla are sending out different builds to get a variation in their test data.
 

Bluebell

Member
Jul 12, 2019
100
68
Oxfordshire, UK
2020.32.5, no FSD.
The car consistently slows when the speed limit reduces but does not always speed up when the speed limit increases. It could be as suggested above, it depends on the speed limit when AP was first engaged.
 

Steggi

Member
Mar 15, 2020
14
4
Norwich
I have noticed my car will want to do 40 in a 30 coming out of whymondham as the speed limit has been dropped to 30, car still sees it as 40, guess this is a GPS map speed. It picks the 50 zone up but carries on at 30.
A section of the A140 north of Norwich the cruise control will slow for the 50 then take its self back up to 60 when in the 60 again.
I’ve also noticed that leaving the A11 onto a slip road the cruise control will drop the speed in 5mph increments down to 25mph and the car will slow down to each change.
 

VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,757
6,326
Surrey, UK
I have noticed my car will want to do 40 in a 30 coming out of whymondham as the speed limit has been dropped to 30, car still sees it as 40, guess this is a GPS map speed. It picks the 50 zone up but carries on at 30.
A section of the A140 north of Norwich the cruise control will slow for the 50 then take its self back up to 60 when in the 60 again.

Nothing consistent there. Is the A140 incident a temporary limit or permanent?

I’ve also noticed that leaving the A11 onto a slip road the cruise control will drop the speed in 5mph increments down to 25mph and the car will slow down to each change.

I think the above is likely to be fleet speed. Its been around for some time and is what slows cars for corners, intersections and off ramps. Its possibly also what is responsible for some phantom braking events - those that occur when a car travelling on fast road is passing next/below an intersection at end of offramp - possible that GPS and/or mapping not accurate in these scenarios so it thinks that it is somewhere it is not.
 

Steggi

Member
Mar 15, 2020
14
4
Norwich
Nothing consistent there. Is the A140 incident a temporary limit or permanent?



I think the above is likely to be fleet speed. Its been around for some time and is what slows cars for corners, intersections and off ramps. Its possibly also what is responsible for some phantom braking events - those that occur when a car travelling on fast road is passing next/below an intersection at end of offramp - possible that GPS and/or mapping not accurate in these scenarios so it thinks that it is somewhere it is not.
The A140 speed is a permanent speed limit. The car has suddenly braked a couple of times passing slip roads, is this phantom braking? The first time it suddenly braked a van narrowly missed crashing into the back of me.
 

MacJester

Member
Aug 11, 2019
88
26
Cranbrook
Mine M3LR with FSD will slow down and speed up as the limit changes (albeit some distance after for both) on autopilot but won’t change speed on NOA even if it knows the limit has reduced (eg on the 50mph limit motorway from the M25 to Blackwall Tunnel).
 

VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,757
6,326
Surrey, UK
The A140 speed is a permanent speed limit. The car has suddenly braked a couple of times passing slip roads, is this phantom braking? The first time it suddenly braked a van narrowly missed crashing into the back of me.

Most likely. Seems to occur if mapping/GPS location is off. Not sure what maps you have but later may improve things, or not.

Mine M3LR with FSD will slow down and speed up as the limit changes (albeit some distance after for both) on autopilot but won’t change speed on NOA even if it knows the limit has reduced (eg on the 50mph limit motorway from the M25 to Blackwall Tunnel).

The release notes say 'local roads' only, whatever they are exactly. In my limited experience, if the car is on a road that supports NoA, its totally blind to the speed signs.
 

ParHunter

Member
Nov 2, 2020
149
55
Surrey, UK
Moderator comment - following part of thread merged from "Confused about cruise control"

I often use the adaptive cruise control in 30 zones when they have a few speed cameras. The other day I’ve noticed that the speed went up to 40 when I got into a 40 zone and then decreased again when I‘ve entered a 30 zone. I thought ’Oh that must be new’ as I had the understanding that it keeps the speed you set it with.

The thing is this seemed to be a one-off. Now it just keeps the speed you set it to again. Is there a mode where the cruise control adjusts itself or was the car just having a mind on its own?
 
Last edited by a moderator:

init6

Member
Oct 16, 2020
763
452
Scotland
I think there is an option to choose either 'current speed' or 'speed limit' for TACC. Would have to look at the manual to confirm though.
 

Pink Duck

Member
Jan 28, 2020
116
59
South Norfolk, UK
On my S the cruise target can be manually adjusted but then it won't auto follow the speed limits. If it's at say 30 mph but manually then a 2-second pull on cruise stalk will keep it as 30 mph but then start to track database or visually recognised sign changes, albeit with the usual delay.

Sometimes the database of speed limits has glitchy small segments of variable speed limit, which confuses things when in the latter mode.
 

VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,757
6,326
Surrey, UK
I thought ’Oh that must be new’ as I had the understanding that it keeps the speed you set it with.

The thing is this seemed to be a one-off. Now it just keeps the speed you set it to again. Is there a mode where the cruise control adjusts itself or was the car just having a mind on its own?

You and me too. Its simply not consistent for me and I just assume its not going to change speed. But recently I got caught out on M3 after having merged from M25. Its a 50 zone and the car merrily sped up to 70 so I had to quickly intervene. But another time, it sits there quite happily at the correct speed. Whether there is a rule governing how/when it works I have absolutely no idea. But I cannot see any pattern as to whether it will or won't suddenly start working.

Is a little similar with green light chime, a FSD feature. Apart from a very brief section of a journey, this simply does not work for me. But that is one that I will revisit in another topic...
 
Last edited:

Mrklaw

Member
Mar 5, 2020
481
256
Berkshire
One of the first things I did when I got my car last week was setting the cruise to come on at my current speed (I think its a new option under autopilot). Thats what I’m used to and defaulting to the speed limit the car thinks it is would only confuse and frustrate me - also so many 50mph roadworks around on motorways near me that it may not realise
 
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Cardo

Member
Sep 22, 2020
528
370
Surrey, UK
On TACC I have not had any automatic speed changes. I’ve had to confirm the change by tapping on the speed limit symbol, be that to increase or decrease speed.

The behaviour is different on AP. The speed will automatically decrease when entering a lower speed limit. In relation to increasing speed, it seems to depend on what speed you were at when you engaged AP. If the decrease was during AP and it automatically lowered, then this will automatically increase again when going into the higher speed limit, but only as fast as the speed you originally set. If you engaged at 30mph and then enter a 40mph, it won’t automatically increase the speed and requires a tap of the speed limit symbol (or use the scroll wheels).

This is how I believe it works from my experience, anyway!
 

Dilly

Active Member
Feb 24, 2020
2,356
1,893
Norfolk
I agree with other comments. It’s totally inconsistent.
in my experience, TACC alone doesn’t change speed automatically whilst AP does. Having said that, if you set TACC then engage AP it doesn’t change speed automatically. If you engage AP from the off, it does seem to. Somewhere in the mix is the Max speed last set. I’ve had it change from 50 to 30 to 40 but then only back up to 50 in the following 70 limit.

so yes. You’re right to be confused!
 

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