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Speed Control with cruise control.

I have been driving my MY for about a month. I put it on cruise control and auto steer. It does detect the speed limit signs and if I ingage the cruise control it will set the speed limit to my setting of speed limit plus 5. That works great. But if I am cruising along at 65 and suddenly the speed limit changes to 45 or 50 the car does not slow down. The set speed stays at 65. Same in reverse. If I set the speed by touching the speed limit icon it changes speed but if the limit goes to 65 the car will not accelerate and I find myself going 45 in a 60. I thought the car should automatically set the cruise speed to my setting of 5 over whatever the speed limit is. Am I missing something?
 

Tam

Well-Known Member
Nov 25, 2012
10,115
9,205
Visalia, CA
...if I am cruising along at 65 and suddenly the speed limit changes to 45 or 50 the car does not slow down...
I think that is about right. When I purposefully set my speed above the posted sign, I don't want the car to override my decision each time it sees a new signpost.

...speed limit icon...

Speed limit icon on your instrument cluster should update itself in real-time each time it sees a new speed signpost.


...it changes speed but if the limit goes to 65 the car will not accelerate and I find myself going 45 in a 60...
Sometimes my car would not drive as fast as the Speed Limit Icon on your instrument cluster but I would blame that as a bug and it should not be the rule.

...I thought the car should automatically set the cruise speed to my setting of 5 over whatever the speed limit is. Am I missing something?...
Please check your settings: Is it "relative or absolute"?
 
My setting is 5 miles over the speed limit. D see I if the speed limit is 55 my cruise speed is 60. That is fine but if I am cruising at 60 and the spied limit drops via the signs to 45 or increases to 65 my car stays at 60 unless I touch the speed limit icon on my screen. I would think that if the posted speed changes my car should automatically go to the new limit plus 5 as my cruise setting without me having to touch the speed icon on the screen.
 

Tam

Well-Known Member
Nov 25, 2012
10,115
9,205
Visalia, CA
My setting is 5 miles over the speed limit. D see I if the speed limit is 55 my cruise speed is 60. That is fine but if I am cruising at 60 and the spied limit drops via the signs to 45 or increases to 65 my car stays at 60 unless I touch the speed limit icon on my screen. I would think that if the posted speed changes my car should automatically go to the new limit plus 5 as my cruise setting without me having to touch the speed icon on the screen.

My guess is the system is still beta so it's all over the map for now and we still have to drive and adjust the speed randomly as needed.
 

Johnny Vector

Member
Jun 21, 2020
298
491
Maryland
It seems to work differently on divided highways vs. two-way roads. In my experience, on divided highways it stays where you set it, and you have to change the speed setting yourself. On two-way roads (even if there are multiple lanes in each direction), it won't let you go more than 5 mph over the speed limit, and it enforces that by changing the speed setpoint based on speed limit signs. Mostly. Sometimes it messes up and doesn't adjust to the speed limit change. I haven't figured out yet what triggers that bug, but it's pretty rare.

It makes sense to me that the response is different on divided vs. non-divided highways, but it can be confusing.

At least, that's how it has worked for me.
 
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EVEnergy

Member
Sep 2, 2021
47
36
Wyoming
Johnny Vector is right - speed limit works differently on divided highways and 2 lane roads. Divided highway (like an interstate) it will maintain the speed you set regardless of the speed limit sign. On a 2 lane road, it depends on some factors:

* Suppose you engage TACC in a 65 mph zone (it will go 70) and then the speed limit drops to 45; if it reads the speed limit sign, it will drop to 50 and then resume 70 once the speed limit (again assuming it read the sign) increases back to 65
* Suppose you engage TACC in a 45 mph zone and then the speed limit increases to 65; it will stay at 50 because it doesn't know if you want to go the speed limit or stay slower. However, once you manually increase the speed to 70, it will behave like above
* I've found that it's pretty good at reading speed limit signs however, it gets confused if there is a "truck speed limit", it does miss some signs, and speed limits in the nav database can also be wrong which will through things off.
 
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WattsappMTL

Member
Nov 2, 2020
277
260
Montreal
Thanks for the clarifications about speed limit changes. I had noticed that this happens sometimes, but not always - hadn't figured out that it depended on road configuration.

It seems that data from roadside signs is overlaid on speed limits already provided in the navigation database. I've found that the car has trouble with signs that say "ENDS". It reads that value as the active speed limit, which is rather annoying! In this situation, the new speed limit isn't posted so it would have to fall back to a default value for the road, which needs to come from the database.
 
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Johnny Vector

Member
Jun 21, 2020
298
491
Maryland
Thanks for the clarifications about speed limit changes. I had noticed that this happens sometimes, but not always - hadn't figured out that it depended on road configuration.

It seems that data from roadside signs is overlaid on speed limits already provided in the navigation database. I've found that the car has trouble with signs that say "ENDS". It reads that value as the active speed limit, which is rather annoying! In this situation, the new speed limit isn't posted so it would have to fall back to a default value for the road, which needs to come from the database.
I hate those signs! Why are you telling me what the speed limit isn't? I need to know what it is. So stupid.
 
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I noticed also it does not slow down when you you take an exit ramp that has a sign posted. If I take an exit from a freeway where I was going 70 and then I want to exit and the exit ramp has a 45 sign, the only way to slow down is step on the brake which of course disengages the TACC. I wish there was a way to slow down for an exit and then pick up the speed limit from the new road and reengage TACC. It seems I am frequently having to engage and disengage TACC. I know it is part of the driver awareness requirement.
 
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WattsappMTL

Member
Nov 2, 2020
277
260
Montreal
Johnny Vector is right - speed limit works differently on divided highways and 2 lane roads. Divided highway (like an interstate) it will maintain the speed you set regardless of the speed limit sign. On a 2 lane road, it depends on some factors:
Not for me. I played around on a 2-lane road this week and the target speed stayed where I set it regardless of posted speed limit changes (up or down). Perhaps it has something to do with TACC default settings? I use speed limit engagement mode, with a percentage relative offset. The car selected that speed initially and it stayed the same till I tapped the speed limit icon, at whic point it would drop or increase to that value plus offset.
 

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