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Faster Stops

Discussion in 'Model S: Driving Dynamics' started by Liz G, Jul 6, 2013.

  1. Liz G

    Liz G P03056

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    So, I was thinking about this last night as I fell asleep and thought I would post on it.

    It occurred to me that not only does the Model S have a shorter stopping distance it also starts stopping faster than an ICE.

    We all know that when someone does an emergency stop there are a couple of lag points in response time. The first being the time it takes for the driver's brain to register the need to stop and the time the driver begins to move their foot off the accelerator. And the second being the time it takes for the driver to actually move their foot from the accelerator to the brake.

    Now in an ICE, there is no slowing (or very minimal slowing) as the driver removes there foot from the accelerator to place it on the brake. In the Model S, however, as soon as the driver lets off the accelerator to hit the brake, the car starts braking. This means that in an emergency stop, the Model S is, for all intents and purposes, removes some of the lag time when switching from accelerator to brake. Meaning the driver can begin stopping faster in the Model S than in an ICE. True the regen is not as hard of a braking manuveuor as actual braking but it does slow the car quite a bit. And this faster time to begin stopping could make the difference in avoiding an accident or at least reducing the damage caused in an accident.

    So we can add this to one more way the Model S is safer than an ICE.
     
  2. Al Sherman

    Al Sherman It's about THIS car.

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    No question. Might even be significant at higher speeds. It would be an interesting mental exercise for the "math people" on TMC. Anybody?
     
  3. caddieo

    caddieo Member

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    It could also increase the chances of being rear-ended. I believe there was a recent post about a close call of this nature.
     
  4. Raffy.Roma

    Raffy.Roma Active Member

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    In an emergency situation you don't think about the chance of being rear-ended, you only want to avoid any accident. That's the main thing.

    - - - Updated - - -

    Al as you know the Model S has 2 levels of regen. It very much depends upon what level of regen is selected on the car when you decide to stop. If the higher level of regen is selected the emergency stop is very much eased.
     
  5. caddieo

    caddieo Member

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  6. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    Read that first sentence back to yourself. ;) But yes, In a real emergency stop situation you need to hit your brakes instantky. That's why hypermilers and defensive drivers try to avoid being that close: you don't want to be hitting your brakes every time the driver ahead hits theirs. And, given how many people drive way too close another benefit of maintaini g a good buffer is that you can brake more slowly and give Tommy Tailgater and Sally Cellphone more time to react.


    However, while you get some braking you still need the car to switch from regen to friction. How fast is the friction brake?
     
  7. caddieo

    caddieo Member

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    [QUOTE=ItsNotAboutTheMoney;37963.........Tommy Tailgater and Sally Cellphone.........




    I like that. :biggrin: Can we add Terry Texter to the list?
     
  8. Raffy.Roma

    Raffy.Roma Active Member

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    Yes

    @ItsNotAboutTheMoney

    Who are Tommy Tailgater and Sally Cellphone? :scared:

    @caddieo

    Who is Terry Texter? :eek:
     
  9. jerry33

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

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  10. caddieo

    caddieo Member

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    @jerry33- It's based on an accelerometer, not whether you've set them to high or low.

    Gotcha. Thanks.
     
  11. Doug_G

    Doug_G Lead Moderator

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    Yes, I've always felt the Roadster (now Model S) is just that little bit safer because it's decelerating even before you get your foot on the brake.
     
  12. Al Sherman

    Al Sherman It's about THIS car.

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    Correct!

    @caddieo: Just so you know, you can put the rear camera on at night and play with it to see when the lights come on. I've done this a lot (unscientific obviously) and I've found the algorithm to be pretty darn close to perfect for when I personally would like the brake lights to come on. As well as NOT come on for that matter.
     
  13. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    Ever notice how much less braking the regen seems to give you when at highway speeds compared to city traffic? It's not an illusion: the car's kinetic energy is proportional to the square of its speed, so the maximum available 60kW of regen doesn't provide nearly as large a deceleration rate at 70mph as it does at 30mph.
     
  14. mknox

    mknox Well-Known Member

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    My worry has always been that on very slippery roads (i.e. icy winter roads) suddenly letting go of the accelerator could cause the rear wheels to break free resulting in loss of traction and control. I had an accident (went into a ditch - no other cars involved fortunately) when that happened to me in a RWD ICE when the tranny downshifted as I was slowing. The rear wheels lost traction and I went into a spin. It was crazy how fast it happened.

    I've gotten used to "feathering" the accelerator to modulate speed, and on summer roads, it's great. On occasion, when traffic suddenly comes to a stop, you definitely do get a sudden surge of deceleration when you let go of the "gas" quickly.

    I haven't driven the car through serious winter conditions yet, and others tell me it is a non-issue, but I may still be tempted to dial down re-gen next winter. (I would actually prefer a speed-sensitive setting where it keeps it on "low" at speeds above 30 MPH or so and "Normal" at speeds below).
     
  15. jerry33

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

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    I'd think vehicle stability control would make that a non-issue. I haven't had mine through a winter yet, but other cars with VSC are totally solid in that kind of situation.
     
  16. NOLA_Mike

    NOLA_Mike Active Member

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    Or you can display any of the screens which show a graphic of the car (like the charging screen for example) and it will show the brake lights on the graphic when they come on. The screens that display a picture of the car are dynamic and show, in real time, what the car is doing at the time (lights, roof, doors opened, etc.).

    Mike
     
  17. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    Two points, for and against:

    First, for the OP's argument: One of the facts I remember from Driver's Ed was that the rear-ender always is at fault. Put another way, you always are responsible for maintaining a distance between you and the vehicle ahead of you sufficient enough so that, regardless of conditions, you always can stop before hitting it. Now, laws and especially lawyers have changed since I took Driver's Ed, but it's a safe bet to say that it's a really tough hole to climb out of for whoever rear-ends a sudden-stopper.

    Second, against the OP's argument: Sounds like an argument from someone who knows only automatic transmission driving. On the contrary, in a handshaker, you begin decelerating as soon as you lift your foot off the accelerator pedal, just as in a Tesla. And, yes, a lot of us still drive manny trannies. Though regretfully fewer each year.

    Overall, I agree with the tenor of this thread. And I love sounding like an old fart, too. ;)
     
  18. jerry33

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

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    That's because some folks have scammed the insurance companies by pulling in front of a car and then stopping in order to cause a crash. They often have passengers (aka crash dummies) so that they can collect additional medical benefits.
     
  19. cfOH

    cfOH Member

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    On snow and ice, that phenomenon of the rear tires "breaking free" was due to the shift in weight on the axles as your car went from acceleration (or constant speed) to deceleration more so than an automatic transmission changing gears. While stability control will help in the MS, I agree that setting regen to low in low-traction situations is probably prudent.
     
  20. caddieo

    caddieo Member

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