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TACC & Slowdown due to Car Ahead Changing Lane

Discussion in 'Model S: Driving Dynamics' started by ArtInCT, May 17, 2016.

  1. ArtInCT

    ArtInCT Always Learning

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    I have experience this behavior quite a few times and can somewhat figure out how to avoid it...

    While using TACC only, on a divided highway and following the auto or truck ahead I have noticed that when the vehicle ahead and in my lane makes a right hand lane change or especially begins to exit to the right then my S really begins to slow down in a non graceful manner and the "toy car" even shows the brakes coming on. I am not too happy with this sudden deceleration and feel it is uncalled for and not my style.

    I have the TACC set to be pretty far back or behind the leading vehicle.

    The work around I use is this.... when I see the vehicle ahead begin to move right or direction signal a right exit, then I gently apply some accelerator which negates the sudden TACC breaking or slowing down.

    Have any of you also experienced this behavior? If so it this TACC slow down "normal"? And what techniques if any are you using to negate the slow down effect?

    All ears,

    BTW this behavior was on 2.17.37 and also present in 2.17.88
     
  2. xrayvsn

    xrayvsn Member

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    I've noticed the same thing and pretty much use the same solution you do (press the go pedal). If I'm in the far right lane and people are braking while already on the off ramp, it still seems the car will decelerate quite rapidly, even when the vehicle is further ahead than what would normally engage the braking (I wonder if brake lights of the vehicle ahead has a more powerful effect on TACC).
     
  3. jmsurpri

    jmsurpri Member

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    Yesterday I had the strangest TACC experience similar to this. It cleared up today, most likely due to the reboot for the new update. Driving down road with 45mph limit and no car in front of me, traveling at 45mph. Display shows the 45mph sign so it knows the speed limit, and TACC is set to 50mph. When I engage TACC with single pull, car immediately slows down to 20mph. If I goose the accelerator, it recovers and speeds back up to the set 50mph. I was able to repro a bunch of times. Not sure what's going on.
     
  4. GoTslaGo

    GoTslaGo Learning Member

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    Had sudden deceleration issue as OP described, just this weekend. I sent a bug report to [email protected] with location, time, etc...

    I didn't do anything this time, because traffic was light and just watched what the car did. It decelerated to 64 mph, then began to speed up again to my set TACC speed of 71. We were originally traveling at around 68 mph. Had other instances in the past which I compensated with the go pedal.
     
  5. kort677

    kort677 Active Member

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    the TACC only see a something slowing down so it slows you down, it is incapable of discerning that the car in front of you is turning. the easy fix is to increase pressure on the accelerator by using your right foot.
     
  6. zzzzdoc

    zzzzdoc Member

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    Mine does this all the time when I am in the left lane, and the car in front of me pulls into a left turn lane. The car slows down way more than it should, and way longer than it should - long past when the car ahead has exited the lane.
     
  7. ArtInCT

    ArtInCT Always Learning

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    I noticed yesterday the following....

    When in the right hand lane with TACC on and behind a car, that car moved to the next left lane to pass the car it was following.
    My model S did not slow down as it would have if that car was moving to a right hand lane or exiting.
    I watched this behavior twice more.

    So why does TACC slow you down when the car ahead is moving to the right hand lane or exiting but NOT slow down when
    they are passing or moving to the left hand lane..... is it because they are speeding up to do the passing or lane movement?
     
  8. NOLA_Mike

    NOLA_Mike Active Member

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    Yes. TACC is continuously calculating how quickly you are closing the distance between you and the vehicle in front and adjusting based on that - so if the vehcile in front is accelerating or maintaining speed it will be a different reaction than a vehicle slowing down.
     
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  9. ArtInCT

    ArtInCT Always Learning

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    That makes total sense.... thanks Nola_Mike!
     

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