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Model S 85 new gear reduction ratio

Discussion in 'Model S: Driving Dynamics' started by Olle, Nov 17, 2014.

  1. Olle

    Olle Member

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    The Model S 85 top speed changed from 125 to 140 mph after the D announcement. Nice :) But what design change made it possible?

    Two guesses:
    1. taller gearing. Is the taller gearing borrowed from P85D so that they only need to make one version of rear DU gearbox for both cars?
    2. just a better inverter that gives more torque at high rpm, still with the old 9.73:1 gearbox.

    What is it? Let the speculation run wild!
     
  2. AmpedRealtor

    AmpedRealtor Active Member

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    Since the 0-60 times have not changed, I doubt this is anything more than a software change. Also, the design gallery says that both S60 and S85 have 380 HP motors, yet the lighter S60 has slower 0-60 times. Can anyone explain that?
     
  3. Olle

    Olle Member

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    #3 Olle, Nov 17, 2014
    Last edited: Nov 17, 2014
    I noticed the same as you regarding the unchanged 0-60 time. As others have noticed, the 85 really did 0-60 in 4.9. With a 15% taller gearing lets say that brings your 0-60 up 10% from 4.9 to 5.4. Voila, there you have it!

    Software change 120 to 140 mph? no way. They were physically limited somewhere around the listed top speed IMO. It was obvious when you drove it around top speed that you were at the actual torque limit of the motor, as opposed to hitting a traditional governor. Especially since the top speed varied each time. We only tested in a P85 but never hit over 133.6 mph on the best run. sometimes 131. A governor doesn't vary like that. If not even the P85 could do 140, how can the less powerful 85 do it with the same gearing? Please challenge me on this someone, if you come up with a solution.

    Ok, to your question about the 380 hp motors. Why different 0-60 times for 60 and 85? It is because of the smaller battery of course. The motor won't produce 380 hp on the 60 battery for as wide of a rev range as it would on the higher voltage 85 battery.

    I wouldn't put much value in these nominal motor power numbers. It is the motor/battery combo that matters of course. Then there are so many variables that its almost meaningless to quote a combo power number. The old 85 and P85 have been measured by many owners to have way more power than the listed motor/batt combo number, 416 hp for the P85 Some people got up to 470 hp on max acc. But most of the time they had much less, at top speed or with a low SOC battery for example.
     
  4. Blue in NC

    Blue in NC Member

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    Not disputing your idea but anyone willing to trade .5 sec in 0-60 time (potentially used often) for 20 mph on the top end (hardly ever used) is crazy. That would be a terrible choice by Tesla.
     
  5. Olle

    Olle Member

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    Great point. But combined with the cost savings of only one gearbox it might be worth it. How Else did they achieve it?
     
  6. randompersonx

    randompersonx Member

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    Very possible the logic went like this:
    If they promised 5.4 and delivered 4.9 before, but promise 5.4 and deliver 5.4 now, it's pretty easy to make the argument that no such loss happened.

    If you want faster than 5.4, get the P85D...
     
  7. brkaus

    brkaus Member

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    Unless the change was motivated by improved range. The higher top end might just be a byproduct.
     
  8. Olle

    Olle Member

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    I can't believe nobody knows the answer. I thought the basic mechanics of the car was Tesla 101 for the tech savvy forum members :)

    I just saw on the TM Model S specs page that the 60 still has 9,73:1 ratio. There is no spec sheet for the other cars but if those gears still exist in the 60, the theory of saving production cost by cutting that gearbox out doesn't hold. Perhaps an inverter improvement after all.
     
  9. efusco

    efusco Moderator - Model S & X forums

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    I say "Yes Way". I see no reason to think that this isn't exactly what they did. Perhaps there were also some inverter changes made, but everything seems to suggest that the top speed was a software limitation, not a physical one. I suspect it'll take a long time to get there and will be very energy demand heavy, but I dispute your contention that it is not a software change.
     
  10. Olle

    Olle Member

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    here is a, perhaps far fetched, theory for the new 85:
    15% taller gear combined with the old P85 inverter. approximately same acc as old 85 and higher top speed

    - - - Updated - - -

    - - - Updated - - -

    If only a software change, why didn't they do it earlier when they promised an autobahn version of MS last year? Would't the a software change have been part the first thing if the hw was there to support it? Could it be that they have more battery cooling now and therefore allow more top speed? Still I don't understand why the top speed appeared as a soft asymptotic limit rather than a sharp limit, if it was in fact governed. I remember a loaner I had limited to 100 mph. When you hit 100 it was like hitting a wall because it was governed.
     
  11. efusco

    efusco Moderator - Model S & X forums

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    I think lots of reasons.. On the Autobahn the use of very high speeds on a regular basis would be a good justification for a higher gear ratio to improve energy efficiency at those speeds. In the US and elsewhere where those speeds are rarely ever touched, efficiency wouldn't be an issue.
     
  12. scottm

    scottm Active Member

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    Who cares what top speed is, you will never go there. That is stuff for engineers and car magazines to talk about.
    Put the power curve where people can use it, and that is where it is. Taller gearing would just start sapping that away.
    Off the line is way way more useful than top speed.
     
  13. Olle

    Olle Member

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    I hope you are correct. only software means that we will all get it on our current Model S, right?
     
  14. bevguy

    bevguy Member

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    Top speeds on cars are often limited by tire choice, cheaper tires are designed for lower tip speeds. With aerodynamics being so much better today even a Corolla can go considerably faster than it does, it has a speed governor on it.
    I don't know how fast my S85 delivered in march 2014 will go. I'll let somebody else find that out. Super top speeds are useful only in Germany, and not many places there either.
     
  15. slcuervo

    slcuervo Member

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    Fully agree!
     
  16. Adrian

    Adrian Title(D)

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    I regularly travel over long timeframes at my current cars limit (255 kph) when i'm in Germany. Never say never. Traffic traveling at 160 kph is not unusual here over the pond.
     
  17. Olle

    Olle Member

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    This thread is about what design changes made the new top speed possible. Your question "who cares about top speed" is a different subject.
     

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