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Black Ice and Regen: bad combo?

Discussion in 'Model S: Driving Dynamics' started by scottm, Nov 13, 2015.

  1. scottm

    scottm Active Member

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    #1 scottm, Nov 13, 2015
    Last edited: Nov 13, 2015
    No, I'm not showing a picture of my car ditched after hitting black ice patch on highway. Because I kept it on the road. Luckily.

    Your natural reaction when sensing loss of traction on ice is to lift the accelerator pedal.
    Regen kicks in when you do that. Doesn't matter if set to high or low regen, the car dips into the green zone.
    (I set my regen to low for highway driving).
    Regen is like hitting the brakes, but only in the rear (I have S85 not a D).
    Braking in the rear on black ice is ... nerve wracking.
    It creates drag and induces slippage in the rear and the car starts to sway in the rear, and loud CHUNK CHUNK sounds kick out from the rear as ESC and/or other mechanisms of the car back there are realizing the loss of traction and try to lessen the grip of regen.
    And you continue swaying and concentrate on steering the car to keep it on a line.

    When you get it under control, it's time to go clean your pants.

    OK, this would happen on D model too, maybe all four corners start regen and slipping and sway front and rear... Maybe you get smarter "torque balanced" regen and only one end or the other start slipping, and swap slipping duty as front and rear fight for regen duty. Good luck with that! One axle was enough for me.

    Q: What the hell would happen if you were auto-piloting your car and this happened... what would the software do? Well, you shouldn't be using auto-pilot in adverse weather conditions anyway... not even cruise control. Driver beware, your fault.



    Cause of my incident: SUDDEN shift of driving dynamic and brake drag created by regen, even set to LOW. On sudden appearance of almost frictionless ice surface on road. Surprise!

    I could do two things, if I had all my mental faculties working and great reaction time, I could try to NOT LIFT the pedal completely but match speed to energy to be flat-line neutral (not orange not green but flat)... i.e. no torque difference between road and wheel rotation. Good luck with this on patchy ice. NO human could keep this matched using the pedal.

    Or, I could bump the gear selector from D up to N. And coast, and keep off the brakes. I chose this approach, and practiced it on non-ice portions getting ready for the next surprise. But if you bump from D up too hard (double bump) car thinks you are asking for R... and beep-beep warning no way can you do that... and keeps you in D doesn't even go half-way and give you N. You must lightly tap up to get N.

    Easy to do in panic situation, right? Lightly tap up to N... so your rear end doesn't lose it completely and come around the other way. Tap too hard and .. you lose. You get about one shot at this before its too late. And you have to drive with your finger tip on the gear selector, in ready to tap position. Easy to do miles on end.

    I suggest you practice. It's the only thing you can do.

    Until Tesla improves this driving dynamic in software.

    What should Tesla do? TWO THINGS immediately for next software release please:

    1. At least offer a USER CONTROL slider for REGEN selection: OFF. Zero, none, coast when foot off pedal.

    Maybe tie the feature to "Cold whether package" for those of us who face icy roads on a pretty regular basis.

    What else could they do?


    2. When the car is in motion, consider a user input double bump from D to R on the gear lever as a request for N. And put the car in N. Just do it.


    Having the car do a NO CHOICE braking maneuver special on sudden loss of traction surface.... is silly. :scared:
     
  2. thefortunes

    thefortunes Member

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    This is interesting to me because I have the exact opposite reaction with my Roadster on ice....regen is MUCH better (much more quick to modulate) than ABS.

    I have serious stopping issues when my regen is limited due to cold and I have to rely on ABS.
     
  3. JohnQ

    JohnQ Active Member

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    True, this can be an issue. I've trained myself never to fully lift off the accelerator in a panic unless I would normally also slam on the brakes. It takes a long time to break a lifetime of ingrained habit but I've become more accustomed to it. Useful retraining as it pays not to make any quick inputs when dealing with slick conditions.

    Finally, even though I regularly drive in snow and ice, I've only felt in danger of losing control once and that was within a week of taking delivery. Went to pass a car on a two lane road and punched it while aggressively moving the wheel to the left to pass. I was used to the turbo spool up and downshift delay in an ICE. Lots of wiggle in the rear end when I did that. Taught me something about the instantaneous response of the car.
     
  4. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

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    I've learned to deal with the rear tires locking up with regen when in slippery conditions. ESC kicks in to keep the car square where necessary. It is a bit unnerving, I admit, to feel the rear of the car drag like it does.
     
  5. Jaff

    Jaff Active Member

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    Agree totally...I drive my Roadster all year round...it really didn't take a lot of icy road kms to learn this...I do wonder though, with quite a few Model S drivers opting to use low regen for winter driving, whether the larger size of the Model S negatively affects the vehicles performance on ice (when regen kicks in)...My wife thinks it does, and only uses low regen when winter driving.

     
  6. tezzla

    tezzla Member

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    I have no idea what you guys are talking about? Here in So Cal, it rains every once in a while, "black ice" is that some sort of breath mint? :)
     
  7. AWDtsla

    AWDtsla Active Member

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    Should have an OFF setting, as should stability and traction control, as discussed in another thread. Will Tesla do it? Who knows.

    It feels like when Dell/HP started removing the reset buttons from their Windows PC's, delusional. No, autopilot is not an expert slippery surface driver yet, the real driver needs control.
     
  8. sbradbury

    sbradbury Member

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    What tires are you driving on in this black ice situation?
     
  9. PaulusdB

    PaulusdB Mayor Gnomus Vintage Limb

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    Black Ice and Regen, bad combo

    I've got a simple solution for you.

    Pushing the stalk down when the car is in D; this puts it in N.

    I use that procedure for easily switching to coasting, because -yes- it's hard to balance the pedal between power and regen.
    Regen Off is on my wish list as well, as this would allow us cheapskates to optimize energy use.
     
  10. bstronger

    bstronger Member

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    The loss of traction with rear tires also happens in many rear drive cars with rear differentials that
    'hunt' for traction on ice. SOP is to go to neutral or just clutch in. RBS
     
  11. electrish

    electrish I Sing the Body Electric

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    I don't think this behavior is limited to RWD cars, as I experienced a similar situation slowly in my P85D going down an icy road on a steep hill in our neighborhood last Winter and the rear broke out with Regen set to hi. I was on the settings screen and immediately turned it to low, which helped tremendously. This was even with Winter tires, so it seems that Regen favors the rear motor, even on D vehicles.
     
  12. Matias

    Matias Active Member

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    Strange that this is still issue. Tesla should disable regen immediately whan car senses tires slipping.
     
  13. CHG-ON

    CHG-ON Still in love after all these miles

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    That would be terrifying to me. I had a black ice experience many years ago at night. Conditions were clear and I was on a highway with no other cars around in northern Maine, so I couldn't see any reflection on the road to indicate ice. I was going about 50 and a big gust of side wind hit me and rotated my rear end slightly. I flew of the road at fifty into, and through, thank God, a 15 ft snow bank, down and up the median and stopped inches before the other direction road. Amazingly, a tow truck saw the whole thing from the other side, that I was now almost on, and winched me up onto the road. I couldn't start the car. I opened the hood and the entire engine was encased in snow. I had to dig it all out of the bay and the wheel wells and finally got the car started.

    Needless to say, I drove the rest of the way on the shoulder, where there was snow for grip.

    I vote for an off feature!
     
  14. vgrinshpun

    vgrinshpun Active Member

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    #14 vgrinshpun, Nov 14, 2015
    Last edited: Nov 14, 2015
    I believe that there is over-reaction here. The regen is controlled by the car propulsion based traction control the same way as acceleration. Even if drivetrain traction control can't keep car on an intended path (within reasonable tolerance), the ABS will kick in. Ultimately, the car will be held on the intended path, although it will feel unstable while all the systems are working to optimize the response. This concern surfaces time to time, with invariable overreaction (imo), but there were no reports of cars completely going off the road. The feeling of car being unstable while system works its magic is normal, and in itself should is not be a cause for panic.

    I personally never experienced black ice in my MS (actually, maybe, but not that I've noticed). I am running winters on my P85+ (Blizzak LM60), and have no reservations using full regen on slippery, packed snow roads. I tested it quite a few times going about 50mph (mainly in response to alarmed posts about the regen and slippery conditions) and never had any hint of a serious problem. There is sensation of car not being sure footed, but this is inevitable, as ESS operates in response to a disturbance in traction, which will lead to car feeling unstable.

    For the reference, I did a back of the envelope quick calculation a while ago which showed that full 60kW regen is equivalent to about 1/4 of the full on emergency brake application.
     
  15. AWDtsla

    AWDtsla Active Member

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    The car is not letting the driver be a driver, period. In a car like a Tesla where all this functionality is at the whim of literally a few lines of code, the driver should be in full control at all times.

    Add ABS disable to the list.
     
  16. vgrinshpun

    vgrinshpun Active Member

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    Isn't this true for any contemporary car except that it has more latency in the drive system?
     
  17. AWDtsla

    AWDtsla Active Member

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    BMW gives you several levels of disabling traction and stability control, including a mode to allow 15 degrees of yaw angle before stability control kicks in. Also, you have this thing called a clutch that lets you disengage all engine braking.

    So BMW is ahead of Tesla. Regardless of system latency.
     
  18. tom66

    tom66 Member

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    It's worth noting that ABS and regen work together on at least the Model S.

    In accident damaged vehicles with loss of brake fluid and ABS faults, regen is never entered as the car is in "limp mode" and cannot know for sure if regen can be safely activated. Car will just coast.

    This is mentioned in the Stretchla blog, which is worth a read if you're interested in some of the technical details of the Model S.
     
  19. loco

    loco Member

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    I had a similar experience two years ago in P85+. All roads in my town suddenly covered in ice during late afternoon. I think it was some rain and then a sudden temperature drop. On Google Maps all streets turned red. That day I had an appointment to switch to winter tires. I left home and as I was coming to a stop light, I lifted the accelerator pedal. Too much I guess. Tesla started going sideways, as if I had used the handbrake in a conventional car. I tried to counter steer as much as I could, but the curb was very near. I think I bounced off it lightly. No ABS sounds at all. I went back home and was careful with regen in slippery conditions since.
     
  20. Neech

    Neech Member

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    I set Regen to low when the roads are covered in wet snow or when it's icy. It definitely makes a difference.
     

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