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VERY close call today on snowy/icy Interstate 40

Discussion in 'Model S: Driving Dynamics' started by tinm, Dec 29, 2015.

  1. tinm

    tinm 2013 S85 Owner

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    #1 tinm, Dec 29, 2015
    Last edited: Dec 29, 2015
    Driving home today, eastbound I-40, about 10 miles west of the Gallup supercharger exit.

    It'd been generally okay weather from Flagstaff which was 14ºF, and by Winslow it was in the 30s, but past Holbrook the flurries began and the temps dropped to freezing. Then just 10 miles from the Gallup charger, the snow got heavy, like a squall almost. Not sticking, but heavy. I was following an 18-wheeler who was driving carefully. Snow was swirling on the dry road; the truck was doing a good job keeping things clear for me. I stayed about 50-100 yards behind him. We were doing about 65 in a 75, no problems.

    Then the truck takes an exit and is gone. A minute later, snow starts sticking on the road. Soon, the left lane of I-40 is covered in snow, right lane is clear, but getting sticky. I slow down into mid-50s. A minute later, right lane is now two wide tire trails clear, but rest sticky and covered with 1/4 inch. And then within 30 seconds, now I'm at 50mph, and then suddenly the road gets slick, the whole right lane is covered....

    This is where many things happened nearly simultaneously:

    • I let off on the gas very gently, but the regen kicks in, like you'd expect.
    • The regen kicking in turned out to be a bad thing because the laws of physics don't know about regen when it comes to cars and slick roads, they just know about cars, slick roads, and braking, and to the world this regen equated to braking.
    • My Model S begins losing traction.
    • Rear wheels get wobbly.
    • Now I'm beginning to fishtail.
    • All the while a Ford F150 that had been following me at a respectable distance has come right up behind me, and he doesn't seem to notice that my car is about to wipe out.
    • The Model S begins fishtailing, first left, then right.
    • Suddenly, I'm driving at 45 DEGREE ANGLE TO THE ROAD! I quickly steer to correct for this, and the car swings 45 DEGREES THE OTHER WAY!
    • I thought for sure my car was about to spin completely around and roll, or at least wipe out off the road or into the F150 behind me.
    • I make frantic steering corrections and I continue slowing down, car is right out on the very very EDGE of going out of control.
    • My wife was sleeping in the back seat, and she's awake now, observing what's going on. I told her to brace herself.
    • Car is wobbly like you wouldn't believe
    • I continue applying corrective steering, really fast, left, then right, then less left, then less right, trying to get car under control
    • Car is still wobbly, rear end feels like it is like 1/2 inch above the road surface, no contact
    • Can't tell if car is slowing down at all, feels like it is free-sliding on glass
    • Finally F150 truck behind me gets a clue and slows down and gives me room to recover
    • Fishtailing calms down, rear wheels have traction again
    • Front wheels are wobbly, trying to find their way
    • Car back under control
    • Heartrate, oh, probably 200 bpm

    All of above took place in span of about 20 seconds.

    Weird thing: within next 10 seconds, road surface became CLEAR, both lanes, no sign of snow, just wet. Clearly the snow trucks had been out and you could see the line of demarcation where they'd turned on the salt sprinkler, and things instantly melted.

    We take the next exit, the one for the Burger King that has the Superchargers, and park, charge, and assess what just happened.

    The car very nearly lost it. I figured, either crash into median guard rail or right shoulder guard rail -- I figured either was imminent, and that all was lost. Luckily, I was able to quickly regain control of the wild swings.

    Facts: 2013 Model S85, normal Michelin Primacy all-year 19" tires.

    Whew, is all I can say.

    Now: I am wondering if there'd been a way to instantly disable regen. I thought about popping car into neutral but wasn't confident of what might happen. But the regen definitely contributed to the near wipe-out. I'm curious what others would've done in this situation.
     
  2. Todd Burch

    Todd Burch Electron Pilot

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    Glad you recovered.

    You said you let off the accelerator gently--although in this case even if the pedal movement was very slow, the real question is how *much* regen did you allow to kick in? In a situation like that, probably 10 kW or perhaps less of regen would be the very most you'd want to allow--so you wouldn't want to allow much regen at all.

    It's very likely this was just a patch of ice for which almost *any* amount of braking would have triggered the rears to break traction. Obviously, in such a situation it's probably a good idea to set regen to low and to be very careful about letting the pedal out extremely carefully, and not too far. Stay focused on keeping regen torque minimal, which is even more important than the rate at which the pedal moves.

    Ideally, the split second you started to recognize that regen was causing you to lose traction, adding enough accelerator input to coast and just gradually slow down that way would have been the best solution. But given that you did break free, and although scary you managed to keep it under control, I'd say you did a good job given the circumstances.

    Experiences like this help keep us careful the next time :).
     
  3. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    Hope your collective heartbeats are getting close to normal by now, and I'm sure everyone's glad you were able to post what you did....rather than something else.

    This is not the first time members have reported that regen is NOT a friend under those conditions. I don't know how best to suggest when is the appropriate time to anticipate this situation and turn off regen before it's white knuckle time, but I'd strongly suggest all reading what just happened to Tinm give careful consideration of doing that.

    How many miles on those Primacy tires? Do you know your tread depth?

    I can assure you the F150 driver was having as frantic a time as you were, seeing an imminent intimate moment with your car.
     
  4. Panoz

    Panoz Member

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    What an interesting situation - it's almost like slight acceleration would've been better than regen...
     
  5. SabrToothSqrl

    SabrToothSqrl Active Member

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    I've also wondered this. We need a snow/ice mode so Regen doesn't brake hard enough to cause issues...
     
  6. tinm

    tinm 2013 S85 Owner

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    #6 tinm, Dec 29, 2015
    Last edited: Dec 29, 2015
    Primacy tires are about 16K miles old, with tread levels varying from 7/32 to 5/32. I just had them checked & rotated & balanced at a service center within the past week.

    - - - Updated - - -

    Given the split-second rise of the situation, my focus was on steering and letting off accelerator. I didn't think about regen while it was all happening, no time to think.

    It was only afterwards that I realized regen was a factor.

    LESSON LEARNED: on snowy days, I will set Regen to Low. :)
     
  7. Vger

    Vger Active Member

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    Certainly, under the circumstances, you did about the best you could, including getting your wife up and prepared. I hope she quickly got a seatbelt on.

    This is a good demonstration of why "all-season" tires are... not! With a car as expensive to buy and to repair as the Model S, especially, I would not dream of driving anywhere snow and/or ice can occur without swapping on real and top-grade winter tires.

    Our similar vintage P85 has driven in similar to worse conditions in the BC mountains last winter, and never came close to losing control. It wears Michelin x-ice3 tires from November through April. My wife wanted even more assurance with her P85D, so we got her Nokian Hakkapelitta 8 studded tires, about the best money can buy. We just drive that car a couple hundred miles through central WA in very similar conditions to what you faced, and never felt so much as a wobble.

    Winter tires are more important that AWD, more important than stability control, more important than anything. If you have no traction, you have no control.
     
  8. tinm

    tinm 2013 S85 Owner

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    Some background....

    This was a 2,650 mile trip, and today's Incident happened on the return leg. We had been monitoring weather conditions for WEEKS. Every day several hours per day, I would check numerous locales all along I-25, I-40 from ABQ to the CA state line, as well as the roads that lead down to Phoenix from Holbrook, through the mountains.

    Every day the forecasts changed. Some days the forecast a week or two out called for huge snow. Then clear. Then warmer. Then rain. Then cold. Then snow again. As the days got closer to the trip, we cancelled some hotel reservations, made others, in anticipation of bad weather. Had we been able to drive all the way down I-25 then cut over to Tucson, we'd have gone that route but there aren't any Superchargers in southern NM yet.

    Finally, the date of westbound NM thru AZ to CA trip arrived. We lucked out. Well, just barely. We got to Holbrook, AZ, and decided to skip Flagstaff and I-17 because of dicey weather. Well, weather got dicey around Payson, AZ. And battery was getting low because of 32ºF temps. So we decided to cut over to Cordes Lakes on I-17. Thru mountains. Following an 18-wheeler. In 32ºF temps the whole way. Flurries and light rain the whole way. Roads never got sticky.

    By the time we got to Cordes Lakes supercharger it was in 40s, then 54 in Phoenix.

    . . .

    During the days leading to home drive, from CA thru AZ to NM, we were going to go Interstate 8, but had new folks to visit in southern NV, so we cut up from El Centro to Quartzsite then up to Needles and up to Laughlin NV. Weather okay all the way. That was yesterday. Flagstaff this morning at 6am was 9ºF. We charged for an hour, then hit the road.

    The Incident that was described at the top of this thread happened just before we reached Gallup today.

    - - - Updated - - -


    Actually she had seatbelt on, even when she was lying down in back. So she was ok, and prepared for the worst. Actually she was great, didn't panic, didn't distract driver.. I was able to fully concentrate on the situation moment by moment and it made all the difference.
     
  9. JeffS

    JeffS Member

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    It is counterintuitive, but the correct action in a sideways slide is to add power. Not much, but a little. It solves the situation much faster than trying to recover with steering inputs alone.

    People who live in snowy states have to teach themselves the proper reaction. It's not something anyone in your situation and geography has to deal with often enough to deal with it correctly.

    Sounds to me like you had about 50% you-did-great, and about 50% you-got -a-bit-lucky. Well done.
     
  10. sorka

    sorka Active Member

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    The Michelins have lousy user survey scores on tirerack:

    5.6 deep snow.
    5.4 ice traction.

    The Cinturato P7's on the other hand:


    8.0 deep snow
    7.9 ice traction

    Obviously an all season isn't going to be as good as a dedicated snow tire, but there can be a *huge* variation in these conditions among different M+S tires and the stock tires have one of the worst scores for M+S tires.
     
  11. mspohr

    mspohr Active Member

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    Putting it in neutral will disable regen. Some people have reported that this is the best way to recover from a slide.
    I have a D and have never had this problem but I remain alert to switch to neutral if necessary.
     
  12. anxman

    anxman Member

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    I would strongly suggest getting winter tires. I would never drive a Model S in icy weather without them. Better to burn through tires a little more quickly than to risk traction IMO.
     
  13. JeffS

    JeffS Member

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    Never switch to neutral. No one with training ever does that. And AWD does not protect against getting sideways on ice. The absolute only benefit to AWD on ice, is getting moving from a stop. Beyond that, it is actually a hindrance. One of the biggest drawbacks to AWD is the false sense of security.

    Nothing about AWD does anything to slow momentum or stop.

    The OP was trying to slow momentum.

    Proper Tires help enormously. But even tires are useless if you don't know how to use them. Putting it in neutral is the worst possible thing to do.
     
    • Like x 1
  14. mspohr

    mspohr Active Member

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    People without D always seem to want to diminish the performance of AWD. Having lived in heavy snow country for 35 years and driven a wide range of AWD cars,I appreciate their superior ability to stop,go and steer in all conditions. You may be happy with your RWD but I will always choose AWD for better performance in all conditions.

    - - - Updated - - -

    As far as putting it in neutral, some have made this recommendation I have never done this and never felt the need. My D has always been solid in all conditions just like dry pavement. The stability control of the car does a superb job in all conditions (at least that has been my experience with the D.)... YMMV
     
  15. JeffS

    JeffS Member

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    The absolute only benefit to AWD in adverse road conditions is the ability to start from a stop. End of list.

    Spend your money however you want. But please don't justify it with false information about ice handling.

    Trucks do better with 4 or AWD because they have ground clearance. The nemesis of a performance sedan in snow and ice has nothing to do with how many or which wheels spin. The nemesis is ground clearance. We don't have it. No matter which version your Model S. We just don't have it.

    On a track in great conditions, AWD accelerates faster and can do more than the rwd version.

    I promise...it is incorrect to state that I am justifying owning a rwd S by minimizing the benefits of AWD. I have never considered anyone's opinion of my expenditures. Ever. So its not that.

    Vehicles driven by professíonal drivers are almost never AWD. Monster trucks and off road racers aside... Professionals learn to operate their vehicles with incredible skill and capability... With one drive axle.
     
  16. PRJIM

    PRJIM Member

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    Does disabling traction control turn off re-gen? Need to try that on my Model S. My old Mercedes has something called ESP where it would work with the ABS unit to limit fish-tailing. I thought all modern cars had this built in. This was separate from Traction Control. Interestingly enough the Roadster handles very well in the snow (better than the Model S) the Continental traction control system is superb. Wonder if a LSD would have helped?
     
  17. David99

    David99 Active Member

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    I did almost the exact same thing just the day before! Also on the I40. I was lucky to get the car under control after going almost sideways left and right. Regen on slippery roads is a really bad thing. After I had my moment I tested out regen in different situations to figure out if tracktion control would kick in. Nothing. The Model S doesn't seem to take regen into account when trying to keep the car on the road in slippery conditions. In all my tests the car started to fish-tail. Sometimes switching regen to LOW helps a little but not when it's just slippery. Regen will automatically reduce itself once the wheels rotate slower (regen is reduced with decreasing speed) but in most cases that's still enough to make the wheel slip.

    After my moment I drive extremely careful with two fingers on the gear stalk and I practiced a few times to switch to Neutral quickly when there was any hint of the car loosing traction. Switching to neutral instantly helps! I really wish there was an OFF switch for regen on slippery roads.
     
  18. JeffS

    JeffS Member

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    I don't think so. I will try that as well.

    As I was pondering professional drivers, I thought about what I would experience if I slid off the road in my RWD Model S.

    I think my first responder would probably be WI State Patrol, arriving in their RWD Crown Vic. Followed by the RWD flat bed to winch me out. After loading onto the flat bed I would probably have to call a taxi and those are usually 2wd as well. That made me go hmmm... Police officers and the diehard Crown Vic. Never see those in the ditches in a snow or ice storm.
     
  19. mspohr

    mspohr Active Member

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    Where I live in CA, all CHP, tow trucks and taxis are all AWD... And most personal cars,too.
     
  20. JeffS

    JeffS Member

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    Hmmm.
    That's unusual. Where we have severe winter, just the opposite. Even on reality shows, in areas including Alaska, troopers in Crown Vics. Not sure what it all means. But for sure, it means that severe winter weather areas, RWD works good enough for professionals including police officers.
     

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