# Adaptive cruise control based on legal speed?



## r-e-l (Dec 19, 2018)

Am i missing a setting?

I know I can set Adaptive cruise control to be a fix MPH above or below speed limit (my default) . I know I can express the same in % (above or below speed limit).

All good.

But I am looking for that speed to be set based on the legal speed. for example, am driving on a road with 35 MPH and the road changes to 40 MPH , I need to retouch the on screen to set the new speed limit. I think its the same the other direction (road changing from 40 to 35 mph).

I would love for the car to change the speed base on the speed limits. I have to assume this is how it will work for FSD so why not offer it as part of the Adaptive cruise control system?

unless it already there and i am missing it .... there was some update in this area last month but I couldn't figure out what was new ... (always drove +2 base on space limit so that wasnt it).


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## Bigriver (Jan 26, 2018)

It does automatically adjust downward on secondary roads where they have it hardwired that it can’t be more than 5 mph above the limit. I agree that I would like that to be a more generalized option as the speed limit goes up on secondary roads, and up/down on all roads. I immediately think of a highway that I drive often where the speed limit changes up and down for no particular reason that I can see. Would like not to be that clueless driver putzing along at an obscenely low speed because I missed seeing one sign.


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## Long Ranger (Jun 1, 2018)

r-e-l said:


> Am i missing a setting?


No. Traffic Aware Cruise Control (TACC) won't automatically adjust up and down with speed limit changes. If you have Autosteer enabled, then it may automatically slow to speed limit + 5mph depending upon the road type.



r-e-l said:


> I need to retouch the on screen to set the new speed limit.


Touching the screen is an option, but I find it awkward. I much prefer using the right scroll wheel. If you spin it rapidly, it goes up or down to the next 5mph interval, and you can fine tune in 1mph increments with single clicks. Alternatively, you can hold down the stalk for a half second to change your current TACC speed to speed limit + your offset.



r-e-l said:


> there was some update in this area last month but I couldn't figure out what was new


It added the options to set to % of speed limit or to your current speed. It also separated this TACC speed setting from the "you're going too fast" warning speed setting.


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## Kizzy (Jul 25, 2016)

This is so annoying! I have one stretch of road where I get to a point where the speed is 50, but then it drops several times. I leave it at 5 over so that when the speed limit does increase, the car will up the speed to 5 over the limit until it reaches that original max speed.

This is not ideal as I don’t want to be 5 over, and if I manually reduce (or need to take over steering during any portion of the route), I lose that higher initial max speed.

This would be a nice quality of life change but is not a major deal breaker or anything. 🙂


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## skygraff (Jun 2, 2017)

While it seems to sometimes adjust speed based on GPS/signs, it’s cerainly not consistent or reliable. I used to always touch the displayed speed limit sign or use the scroll wheel but recently learned that holding down the gear/AP stalk (not sure on cars with separate AP stalk) for a moment does the same as touching the speed limit sign so that’s really easy to do while holding the wheel.

Agree that it is a critical function for FSD.


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## Jason F (Jul 6, 2018)

skygraff said:


> While it seems to sometimes adjust speed based on GPS/signs, it's cerainly not consistent or reliable. I used to always touch the displayed speed limit sign or use the scroll wheel but recently learned that holding down the gear/AP stalk (not sure on cars with separate AP stalk) for a moment does the same as touching the speed limit sign so that's really easy to do while holding the wheel.
> 
> Agree that it is a critical function for FSD.


Yeah it will adjust your speed down only. I agree it should follow the speed limit signs or map data up or down. Not sure why it doesn't. It initially sets that way so different. Driver is still responsible to monitor the car's speed.


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## RickO2018 (Mar 13, 2018)

Bigriver said:


> It does automatically adjust downward on secondary roads where they have it hardwired that it can't be more than 5 mph above the limit. I agree that I would like that to be a more generalized option as the speed limit goes up on secondary roads, and up/down on all roads. I immediately think of a highway that I drive often where the speed limit changes up and down for no particular reason that I can see. Would like not to be that clueless driver putzing along at an obscenely low speed because I missed seeing one sign.


This only occurs when FSD is also engaged.

I'm no programmer, but it seems like a line or two of code is all that's needed. "If legal speed is X, increase or decrease TACC by X+ or - the difference!"

Only theory I have is that if the driver doesn't notice a speed limit change, Tesla doesn't want drivers surprised by unexpected increases or decreases in speeds.


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## DocScott (Mar 6, 2019)

RickO2018 said:


> Only theory I have is that if the driver doesn't notice a speed limit change, Tesla doesn't want drivers surprised by unexpected increases or decreases in speeds.


I think it's just that Tesla wanted another distinction between AP and NOA.


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## Kizzy (Jul 25, 2016)

RickO2018 said:


> This only occurs when FSD is also engaged.
> 
> I'm no programmer, but it seems like a line or two of code is all that's needed. "If legal speed is X, increase or decrease TACC by X+ or - the difference!"
> 
> Only theory I have is that if the driver doesn't notice a speed limit change, Tesla doesn't want drivers surprised by unexpected increases or decreases in speeds.


It should be an option. I know I'm repeating myself, but the car basically has that ability if you're transitioning from a higher speed to a lower speed and back up again while Autosteer is enabled.

If you set speed at 54mph in a 50mph zone with AS enabled the car will do the following:

Switch to 40mph in 35mph zone
Switch to 50mph in 45mph zone
Switch to 54mph in 55mph zone


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