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Black Ice and Regen: bad combo?

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

  1. Wackybroad

    Wackybroad Member

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    :scared: Thanks for your answer! BUT Holy cow.

    Yes, I always come off both pedals. So I guess thats good?

    Another thing. speaking of bad weather...what about snow? Does anyone use snow tires?
     
  2. mknox

    mknox Well-Known Member

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    I have to agree. I have encountered extraordinarily slippery road surfaces that were not readily apparent at all. Years ago, I was involved in an accident where the car in front of me spun around 180 degrees and hit me head on. I remember the police cruiser pulling up and when the cop got out of his car, his feet went right out from under him and he was flat on his ass. It was just past sunrise, and maybe it was the lighting, but the asphalt just looked like asphalt.

    But sure... if it's way below freezing and the road looks "wet", it is clearly safe to assume that it's ice and not water.
     
  3. green1

    green1 Active Member

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    In most vehicles that's not a bad idea, better yet would be putting it in neutral. Even off both pedals there is still some driving force or resistance on the drive wheels, it's much less than with the pedal depressed, but it's still there. The goal in a skid is to get rid of any resistance to the wheels turning so as to allow them to match what the road is doing and regain control.

    On a Tesla it's a bit different, your ideal would still be to throw it in neutral, but failing that you need to try to zero out the accelerator pedal rather than pull your foot off completely, it's a bit more delicate. That said, one of the biggest rules in all vehicles, Tesla included, in slippery conditions avoid sudden movements, that includes not only sudden acceleration and braking, but also sudden removal of your foot from the accelerator, it's all about gradual, cautious movements.

    "snow tires" aren't so much the thing as "winter tires" are. most places we all drive on a regular basis see snow plows, and even if not, the traffic packs the snow in to ice pretty quickly. Even dismissing that, it's a whole lot better to be stuck in deep snow unable to get going, than it is to be on a sheet of ice unable to stop. So the big thing is always about slippery conditions. If you regularly drive anywhere that experiences temperature near or below freezing (even if you don't get much snow), winter tires are essential. They are the single best thing you can do to improve your car's winter performance, even better than upgrading to AWD. And the best part is that they're dirt cheap, you can pretty much ignore the cost of the tires themselves because by swapping between two sets (summer and winter) each set lasts twice as long, that means your only cost is really the rims and the swapping, and swapping can be done by most people in their garage at home.
     
  4. DFibRL8R

    DFibRL8R Active Member

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    I agree about avoiding sudden movements as a good rule of thumb to avoid triggering a slide/loss of traction but most of these slide incidents start when a driver fails to recognize a road surface that is icy and makes a maneuver that exceeds the limits of available traction (we can argue if that's inattention, stupidity or truly a situation even the most expert driver could face). In any case, the slide is already in progress so now what?
    I would suggest it might be better if the Model S driver in this situation focuses on safely steering the car out of danger and targeting whether they want to maintain speed or reduce speed based on approaching collision hazards. This would allowing the car's sophisticated TCS to manage executing what the driver wants. Adding another element in an emergency situation such as the driver physically disengaging the drive unit by switching into neutral or taking their eyes of the road to watch their power meter to find the neutral spot with the accelerator pedal seems like an unneeded distraction.

    To me the issue is once the driver and the car recognize a slide in progress, why should the driver try to outthink the TCS in regards to how power/braking are being applied to the road surface?
     
  5. green1

    green1 Active Member

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    Taking eyes off the road to look at the power meter is indeed a bad idea, my point was more that they need to be gentle on the accelerator, not extreme on or off.
    Putting it in neutral is still your best bet however, and is far from a complicated manoeuvre on these cars, it's a simple flick of the right stalk,

    Think of it this way, the car's traction control and abs is trying to fix a problem despite your inputs, removing your inputs makes it even better. This allows you to focus on steering, and attempting to gradually brake the old fashioned way, which are your two best activities in this situation. Adding the extra complexity of the motor inputs to the situation just adds unnecessary extra challenges to overcome.
     
  6. chickensevil

    chickensevil Active Member

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    It seems to make sense, but I still am not buying that this is, in fact, the best course. If you are indeed trying to slow down or stop while already in a slide, the better thing is regen or regen combined with physical brakes. Because regen is able to be more easily modulated by the computer to apply braking to the system in the same way that ABS works, only better. And if you are in a slide you want to have that slide corrected which means at some point you either need to apply forward power or braking power and to do *that* you need to be in drive, not neutral.

    Yes, it seems scary that as it is doing full regen you feel the slip and the car modulating the regen power, but this is no different from trying to hit the actual brakes and feeling the ABS kick in and the car doing some what of a slide. The beauty of regen is it is much easier for the computer to change the amounts of power draw rather than manipulating a physical braking method with electronic control. (think light switch on and off vice physically screwing in a light bulb and then unscrewing it). Second should you need to change course and go from braking power to acceleration power, you have that option readily available on your right foot through one pedal (without dealing with the lag between moving your foot from one pedal to another). You don't need to look at the dash to know if you are slowing down or speeding up you can *feel* that happening as your momentum is either picking up or slowing down. So simply apply more or less pressure to the pedal to achieve the desired result and the computer will do the rest!

    Neutral removes all of that from you leaving you with the outdated and slow physical brakes and nothing else.
     
  7. green1

    green1 Active Member

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    My suggestion was for the average driver. For the majority of people touching the accelerator before regaining full control is a bad idea, skilled high performance drivers are able to do better, however most can not. Applying brakes (even regen) before steering back in control is also a bad idea for the average driver, the brakes are still available in neutral should you need them, but adding a second type of braking to the mix only adds to the complication.

    Again, a very talented driver can do better using all the inputs, the average driver can not. Studies have shown the safest course of action is to put it in neutral, regain control with the steering wheel alone, and minimal braking only if absolutely necessary, and then re-engage drive only once full control has been restored.

    Unfortunately most people believe they are above average.
     
  8. brianman

    brianman Burrito Founder

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    "Gentle but deliberate" transitions are better in any vehicle in "hostile" environmental conditions. Extreme tends to unsettle the car (and passengers).
     
  9. green1

    green1 Active Member

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    The difference in the Tesla is that gentle applies not only to the speed of the transition, but also to the extent of it, in an ICE your best bet is to gently fully remove all force, in the Tesla you are best to keep gentle pressure applied to try to stay near the "zero" point on the pedal.
     
  10. DFibRL8R

    DFibRL8R Active Member

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    I think this is the take home point, if you suddenly remove your foot from the accelerator in full region mode, the Tesla will attempt to maintain traction AND actively slow you down. Assuming you want that (tree approaching) great but if not modulating the regen back towards neutral would help the car know that the driver doesn't need reduced speed, just a restoration of traction. It seems like regaining traction/eliminating slide would be easier for TCS to accomplish than the combined task of eliminating slide plus reducing speed. Actually putting the vehicle in neutral via the right stalk could hamper the TCS's ability to to provide power input to the drive wheels and recover from a slide (guess here, I don't know how the system is designed in this regard) leaving only TCS application of braking to overcome the problem.
     
  11. Olle

    Olle Member

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    I have done a lot of winter driving up in NY in snowy and icy conditions and don't recognize these concerns about regen. To me it felt like the stability control always took care of it, even when regening on black ice. Sure the wheels locked up but the control system immediately released and put the car back in its intended trajectory every time.

    Has anybody in reality lost control because of regen?
     
  12. chickensevil

    chickensevil Active Member

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    I think this was what was attempted to being asked earlier by someone and noone has responded that they actually ditched their car, or put it in a very bad situation. And I have seen some videos even of this guy driving down hill around a bend with an individual right on his tail, while approaching a vehicle ahead and an oncoming car. Basically a recipe for a disaster of the worst kind. You see in the footage where his tail kicks out a little from the turn, but the driver is able to retain control of the situation and avoids causing any issues all the while actually letting himself get closer to the car he was following as the guy behind him was not so lucky on holding the road as well and nearly misses the Tesla driver before he too is finally able to come to a stop.

    If someone has legitimately lost control in the their Tesla under such conditions I would love to hear what the circumstances were that prevented the car from functioning properly. The worst I have experienced in the car was an inability to climb a hill. In that situation the car just kept reducing power until it stopped giving any power at all, since it wouldn't give power without knowing it could maintain wheel grip. The end result being that you have your foot to the floor and the car just sits there. I have also slid about a foot down my personal driveway while going under 1 MPH (it is a REALLY steep driveway), which there isn't really anything the car can do to help that one and almost put the car into the fence (It is also a really narrow driveway). But out on the open roads? No issues. I say if I can make it out of my neighborhood (lots of hills and such) 1/2 mile to the highway, then I can pretty much take the car anywhere from there. If I can't get out of my neighborhood then the roads a *REALLY* bad and noone is going anywhere.
     
  13. Lyon

    Lyon 2016 S P100DL, 2016 X P90D

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    Yes, many folks, including myself have snow tires on the car in the winter. It's been discussed at length here.
     
  14. dhanson865

    dhanson865 Active Member

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    #94 dhanson865, Nov 20, 2015
    Last edited: Nov 20, 2015
    Welcome to planet Earth mr alien. There are a wide variety of conditions here on this planet.

    Here in Tennesse I've seen what I'd call "clear ice" not "black ice" tons but only rarely have I felt it when I couldn't see it. But believe me I have been on pavement that I couldn't stand or walk on that I could not tell had ice on it.

    Forget seeing it from a car. I couldn't see it when I was on my hands and knees.

    I didn't log the temp and humidity because back then we didn't have the internet in our hands wherever we go. But I'd agree that there is no single temp range or scenario for creating clear ice.

    I'm far enough south I've see rain falling at 50-70F water temp, with air temps above 32F, and ground temps below 15F and water freezing on contact. Solid ice as far as the eye can see.

    I've seen it much less obvious with random water, air, ground temps producing ice in some places and no ice in others. Cross a bridge that is dry only to find a few thousand feet of ice covered road that I had no idea how it got there and not on the bridge I just crossed.

    I've seen random clear ice I couldn't see from the car but could see when I got out and stood on it. I've seen the other way around. I've felt some I couldn't see either way.

    - - - Updated - - -

    Wrong, so wrong.
     

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