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Traction off the line vs at 40mph...

Discussion in 'Model 3: Driving Dynamics' started by WilliamG, Sep 11, 2019.

  1. WilliamG

    WilliamG Active Member

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    So I’ve noticed in my Model 3 Performance that gunning it off the line to ~60mph results in zero traction loss, even in the wet. I’m sure there’s some power holdback, but I can’t really tell. It’s a bullet. And it’s witchcraft.

    However, gunning it at 40-45mph in the wet definitely results in traction loss and some wheel spin straight away.

    Does anyone have any insights as to why this is? I’d expect more wheel spin off the line than at 40mph...
     
  2. Phlier

    Phlier Bluebird

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    Hmm... I didn't know about the 40-45 wheel spin when wet. Next rainy day ( I live in the desert, it's gonna be a while), I'm gonna have to go play...

    I really don't have anything to add, other than I'm really surprised by this.
     
  3. AlanSubie4Life

    AlanSubie4Life Active Member

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    #3 AlanSubie4Life, Sep 11, 2019
    Last edited: Sep 11, 2019
    I’ve never noticed this but it seems possible. I would guess it has to do with one or all of 1) traction control tuning 2) the distribution of torque to front and rear motors vs. time elapsed after accelerator application 3) distribution of torque to front and rear vs. speed and 4) some sort of suspension and drivetrain dynamics due to jerk, which may be ameliorated when doing a launch from 0mph, due to the intentional slow ramp of torque at 0mph.

    To first order, max available torque (and acceleration) is constant to about 45mph. However, from 0-3ish mph, the torque and acceleration ramps up “slowly.” So there is inherently less available jerk, for sure, when launching from 0mph. I’ve never instrumented a “launch” from constant 30mph to higher speeds - maybe there is more “available” jerk (though there may be intentional smoothing in that case as well).

    Anyway, those are my thoughts for some possibilities. I for sure would not expect this same thing to happen when jamming the accelerator at 60-70mph because there is substantially less torque available there due to having reached the power limit around 45mph.

    When the nose of the car dynamically rises on a sudden throttle application, there is a lot of weight transfer going on. Very hand wavy but seems conceivable that it might temporarily break the rear wheels loose if the weight has not fully transferred.
     
  4. WilliamG

    WilliamG Active Member

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    Thanks for chiming in, Alan. I wonder if it's because off the line the car has full AWD enabled because it "knows" this is a high-torque scenario, and at higher RPM to save power it's more FWD or RWD biased (it felt RWD-biased in that momentary test). At 70mph up I doubt there'd be any traction loss since it's so much slower from 70mph onward.

    In the dry, there's no traction loss at any of these speeds.
     
    • Informative x 1
  5. Daniel in SD

    Daniel in SD Active Member

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    Maybe the tires have less traction at higher speeds in wet conditions. Probably related to how a car is more susceptible to hydroplaning at higher speeds. Just a guess. Theoretically traction is the same at 0mph as it is 40mph and acceleration/torque is the same on a Model 3 (except for the initial ramp).
     
    • Informative x 1
  6. AlanSubie4Life

    AlanSubie4Life Active Member

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    This is the simplest explanation and probably the most likely. There have been very heavy rains and flooding in Seattle over the last few days so under those conditions I would expect that you might have some hydroplaning. Maybe @WilliamG can tell us whether it was just wet pavement or pavement with lots of water. Though perhaps a traction difference in wet conditions at speed would still explain it, even if it's not really wet.
     
  7. WilliamG

    WilliamG Active Member

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    Thanks, all, for the replies. It was post-rain wet pavement.
     
  8. KenC

    KenC Active Member

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    The transmission shifts at 40mph, and the process of double-clutching creates some wheelspin. You have to have superspidey senses to feel it, cause it all happens in nano-seconds.
     
    • Funny x 3
  9. ewoodrick

    ewoodrick Active Member

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    Look at some of the videos of people in the snow flooring it off the line. Traction control kicks in and the wheels just won't spin.

    At 40, it's possible that it is a slip that it's having problem recovering from.
     

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