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Traction in snow on summer performance tires

Discussion in 'Model S: Driving Dynamics' started by achaar, Jan 6, 2015.

  1. achaar

    achaar Member

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    I am reposting most of this from the Mid-Atlantic sub forum.

    I have the summer performance 21s and today was awful. We had a couple of inches of snow but the car was very erratic. I got up a hill ok, but couldn't get the car moving after stopping at a light. Flat road, the car would only go sideways. I eventually got it far enough off the road to be safe, but sat there for about 10 minutes rocking it back and forth, but could not get it moving. Finally, I turned OFF traction control, and like magic, I was moving again. I seen many posts about this great traction control system in the car, but I think it was kicking in way too soon, and not letting the car move. I left it off, all the way home. The odd thing was that the car seemed to continuously pitch left while driving, with T/C on or off. Got me thinking of selling my + for a D.
     
  2. Forty Creek

    Forty Creek Member

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    .... or investing in a good set of winter tires. I find that the traction control works really well. Stopping that heavy car in slippery conditions is more of a challenge.
     
  3. dsm363

    dsm363 Roadster + Sig Model S

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    You are on summer tires on snow. Very dangerous as you found. Simply get some rims and put winter tires on it or buy Tesla's winter wheel package and you'll be good. Of course if you're looking for an excuse to get a P85D why not?:smile: You'd still want winter tires or at least all seasons on snow with the D too though.
     
  4. drsaab

    drsaab Member

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    I drove in the snow today on 19 inch michelin all seasons. It worked great. Saw 7 bmw with summer tires. All stuck.
     
  5. achaar

    achaar Member

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    Of course I understand that I am not using the appropriate tires. What I failed to convey in my post was that the car acted very unusually. When trying to drive straight on a flat road, it kept pulling to one side, as if only one wheel was driven. I put the regen on low, and when coasting, the car would alternate between the green and orange, repetitively lurching to one side. And yes, I am looking for an excuse to get the D.
     
  6. EarlyAdopter

    EarlyAdopter Active Member

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    This has nothing to do with the drive train and everything to do with the tires. Driving a D with summer performance tires on snow will be equally unusual.

    Get some winter tires, or a set of snow capable all season tires (Continental DWS or Nokian WRG3).
     
  7. Alysashley79

    Alysashley79 Member

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    The car acted exactly as any car would with summer tires. Mine did the same thing the first time it snowed and I still had my primacys on!! Had my nokian haakas put on the next day and I can sail past 4 wheel drive vehicles....
     
  8. Gabzqc

    Gabzqc Member

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    Winter driving course might help too?
     
  9. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    That is normal for any car with summer tires. The correct answer is four studless winter tires, ideally on their own set of wheels.
     
  10. Doug_G

    Doug_G Lead Moderator

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    Driving on snow with summer performance tires is dangerous. The rubber compound is not designed for those temperatures.

    I once got caught out with Michelin Pilot Super Sports on my old G37 AWD. It was nothing short of terrifying to drive. AWD will not solve that problem. All seasons are barely adequate. Get proper winter tires and you'll be just fine.
     
  11. achaar

    achaar Member

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    Having owned 6 Audi quattro's, I am very familiar with the AWD benefits, and already stated that the tires were not the right ones for the job. Regardless of which tires are on the car, it should not lurch back and forth when coasting. I am more concerned about the non-normal behavior. Thanks for the suggestion about a winter driving course, but I don't feel I need one, and getting into a forum spat about that is fruitless.
     
  12. JST

    JST Active Member

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    Summer tire issue aside, the car was acting like it was one wheel drive because it doesn't have a mechanical limited slip differential. Thus, it really *is* one wheel drive when you turn off the traction control; when one wheel starts slipping, the differential automatically routes all the power to that wheel. That's one of the built-in downsides of a differential. The traction control counteracts this to a limited extent by applying the brake on the wheel that is slipping, allowing the power to flow back to the wheel that has traction. It also cuts the power when the wheels start to slip. But, as you and I both discovered yesterday, there's a limit to what TC can do, and eventually if the ground is slippery enough you just get total immobility.

    I don't think you need the D. I don't think I do, either. I think both of us need good winter tires that will expand the performance envelope in the cold and allow the TC to work more effectively.

    Of course, if you want the D, that's another story. But snow mobility in a RWD P85 on winter tires is going to be a lot better than snow mobility on an AWD P85D on summer tires.
     
  13. LucM

    LucM Member

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    My S85 with winter tires drove without any issue yesterday in CT. My street was not really plowed but there was only an inch or so of snow on my block. My house is located on a decently hilly part of the street and I had no issues slowing down and turning into my driveway. Did not slip once on ride home.
     
  14. dsm363

    dsm363 Roadster + Sig Model S

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    Isn't as simple as tires with zero traction? I don't get what the issue is. You know you were driving on the wrong tires.
     
  15. Doug_G

    Doug_G Lead Moderator

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    JST nailed it - there's no limited slip differential so the traction control handles wheel slippage by applying the friction brakes. Without that you'll get a wheel spinning on one side or the other as the traction conditions continually change. That naturally tends to torque the vehicle sideways.

    As for the winter driving school, speaking as someone who occasionally volunteers at one... I think even very experienced drivers benefit greatly from doing one. Most people don't know how to control a car when it is past the limit of grip, because they rarely experience it. Also in my experience it's a heck of a fun day.
     
  16. EarlyAdopter

    EarlyAdopter Active Member

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    #17 EarlyAdopter, Jan 7, 2015
    Last edited by a moderator: Mar 13, 2016
    That's a good video. Even more eye opening is their follow up video showing the difference in stopping distances between summer tires and winter tires, both on snow and in the rain. When it comes to stopping, AWD provides zero benefit. It's all in the tires. The difference between the two tires is significant.

     
  17. achaar

    achaar Member

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    Appreciate the comments. I agree that driving schools are almost always helpful, and I have been thru some, and have autocrossed a bit as well. Also agree, that a LSD is very useful. To clarify, the lurching I referred to, was with T/C on. I have also said (multiple times now) that summer tires are not the way to go.
     
  18. point1

    point1 Member

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    Sounds like a great idea, four-wheel drive is just what you need, then you can get even more speed before realizing four wheel drive doesn't help when you need to brake for something... Only winter tires does.
     
  19. dsm363

    dsm363 Roadster + Sig Model S

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    #20 dsm363, Jan 7, 2015
    Last edited by a moderator: Mar 13, 2016
    Winter vs all seasons would be most helpful as that's what most people drive on in winter (all seasons). Definitely agree on the tires. Winter tires are a big benefit.

    - - - Updated - - -

    I think your first post simply confused people. You commented on the horrible traction but didn't ackonwledge that summer tires were a major factor (you have since done that).
     

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