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2014 S85 vs 2017 S75 for road trips

Discussion in 'Model S: Battery & Charging' started by schwedisch, May 31, 2017.

  1. schwedisch

    schwedisch Member

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    I have two Model S, one 2014 S85 and one 2017 S75 (both are RWD). I designated the S85 as my road trip car since it had a slightly larger battery and free supercharging. However, with the recent free supercharging changes, my S75 now also has free supercharging, so the choice of which car to take is not as obvious as it used to be. My understanding is the following,

    2014 S85 - Usable battery capacity 77.5kWh when new, but I have about 5% degradation at 90,000 miles, so that leaves 73.6kWh usable battery
    2017 S75 - Usable battery capacity 72.6kWh hours new, almost no degradation, but let's round down to 72kWh.

    So, it seems that there is almost no difference in available battery capacity, generously the 2014 S85 has 2kWh more battery available, which certainly may be the difference between reaching the next supercharger and getting stuck..

    .... but here is when it gets confusing. When I plan road trips with the two cars, I get wildly different results. For example, one segment on my road trip this summer is Lone Pine, CA to Beatty, NV via Badwater in Death Valley. I calculate the segment using the same parameters, 800 lbs load, 1.1 speed multiplier, 78F cabin temp, 120F outside temp and 10mph wind. The segment is 180.5 miles.

    S75 19" tires - energy used 52.6kWh (292 Wh/mile)
    S85 19" tires - energy used 63.8kWh (353 Wh/mile)

    There is a huge difference between the two cars here, and if they are correct, it makes the S75 the obvious choice. It doesn't seem reasonable to me at all, the cars are almost identical.

    On EVTripping, I get the following result,

    S85 - energy used 52.5kWh (292 Wh/mile)
    S75 - energy used 46.8kWh (260 Wh/mile)

    Are these numbers to be expected? I tried Harris Ranch to Tejon supercharger as well, and I get similar results,

    EVTripping S75 - 42.4kWh (364 Wh/mile)
    EVTripping S85 - 46.7kWh (403 Wh/mile)
    EVTripPlanner S75 - 45.6kWh (393 Wh/mile)
    EVTripPlanner S85 - 52.4kWh (451 Wh/mile)

    Is the S75 really that much more efficient than the S85?
     
    • Informative x 1
  2. whttiger25

    whttiger25 Member

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    #2 whttiger25, May 31, 2017
    Last edited: May 31, 2017
    so
    Something definitely seems off. The S75 calculated efficiency is 292 Wh/Mi (72.6 / 249 *100), while the S85 calculated efficiency is 287 Wh/Mi (77.5 / 270 * 100). This is of course based on the EPA ratings. Regardless, they should be pretty close. I think in reality the S75 should be slightly more efficient than the S85 due to a lighter battery and better aerodynamics of refresh, and if you have the slipstream or cyclone wheels vs the old original non cyclones that's a plus as well, although it wouldn't be enough to really register a difference (which is why these websites don't ask about WHICH 19 inch wheels you have).

    Anyway I see no reason for such a huge discrepancy. I would be curious if anyone else knows something I don't... and yes I'm able to replicate the discrepancy on evtripplanner.com
     
  3. schwedisch

    schwedisch Member

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    I tried messing with the Payload number and it doesn't seem to make that much of a difference either. Adding 200lbs is mostly a rounding error it seems.
     
  4. No2DinosaurFuel

    No2DinosaurFuel Active Member

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    I would change the driving habit to all highway driving on EPA website and see which is more efficient.
     
  5. Lanber

    Lanber Member

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    The 85S will supercharge quicker.
    Also I will bet you will find the 85S still retain 75kwh or close to that useable energy, and of that you have aprox 72 kwh between 100%-0.
    You can check this on a CanBus reader.
     
  6. whttiger25

    whttiger25 Member

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    Would be nice if Tesla let you plan trips in the NAV from point A to B, as opposed to only current location to point A. Then you could see what the car is predicting for consumption, which is usually for me very accurate.
     
  7. daktari

    daktari Member

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    Take both cars on the same trip and make a video reporting the consumption and SOC at the end!
     
  8. whttiger25

    whttiger25 Member

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    That sounds like something Bjorn would do!
     
  9. schwedisch

    schwedisch Member

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    I suppose for my purposes I can just plan a trip to somewhere up in the Sierra Nevada (to get some elevation changes) from my house and see what difference, if any, the two nav systems show.
     
  10. schwedisch

    schwedisch Member

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    Well, judging by the fueleconomy.gov numbers, the 2014 S85 uses 38kWh/100 miles and the 2017 S75 uses 34kWh/100 miles, ie, the 2017 S75 is 11% more efficient than the S85.

    If the S75 is ~11% more efficient, 72.6kWh hours would be equivalent to ~81kWh in an S85, and remember, the S85 only has 77.5kWh available, ie, an S75 should have better range than an S85, yet the rated range on the S75 is only 249 while the rated range on the S85 is 265 miles.
     
  11. Olle

    Olle Member

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    I had 335 Wh/mile lifetime consumption in my P85 and 295Wh/mile on our new 75 so that is a 12% improvement. In addition to lower weight and better aerodynamics I attribute it to the accelerator mapping too. First millimeter you press down on the go pedal P85 feels like it unleashes at least double the power compared to a 75, so you use a lot more energy that way.
     
  12. schwedisch

    schwedisch Member

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    So that lines up with the EPA numbers at ~11%. The curious part though is that the usable battery capacity difference between the 75 and 85 is only ~7.5%, so the S75 should then have longer range than the S85. As far as accelerator response, I can't really tell any difference between my S85 (non-P) and S75, however, I think acceleration itself in my S85 is a tiny bit better.

    I'm wondering how they come up with the range number. For example, the 38kWh/100 miles do not line up at all with the 265 mile range, even if you use the advertised battery capacity or if you use the actual one, so the range number seems to have no correlation with the kWh/100 miles number,

    S85 advertised range 265 miles

    S85 at 85kWh = 223 miles range
    S85 at 77.5kWh = 204 miles range

    S75 advertised range 249 miles

    S75 at 75kWh = 220 miles range
    S75 at 72.6kWh = 213 miles range

    In any case, it seems to me that it is true that cars with the 75kWh battery should have better range than the 85kWh batteries in real world driving, regardless of what the advertised range is. I'm surprised by this.
     
  13. whttiger25

    whttiger25 Member

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    I believe the EPA number of 38kwh/100 miles includes charging losses. i.e. how much electricity comes out of the socket to get the car to go 100 miles. I think charging losses are typically 15-20% at level 2 charging.
     
  14. David99

    David99 Active Member

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    I think the problem might be that the trip planner is using the 75D (dual motor version) as a basis for it's calculation. It is certainly a little more efficient. But since you mentioned both cars are RWD only I'm pretty sure the energy consumption will be almost identical. Weight differences make very very little difference on freeway driving.
     
  15. schwedisch

    schwedisch Member

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    So it is possible then that charging is slightly more efficient on the S75, possibly due to higher amperage charger or different battery chemistry, so what could explain part of the difference in the EPA number. Makes sense.
     
  16. whttiger25

    whttiger25 Member

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    Actually after consulting the EPA website it appears there actually is a substantial difference. They have 89 MPGe vs 98 MPGe for the two models. Also interesting to note that the pre refresh 70 has the same efficiency as the 85. It can't be all aerodynamics, I wonder if they changed the gear ratio or motor with the refresh? You can also see there is a definite difference as well when you add on the dual motor, but it isn't enough to explain the trip planner. It appears the trip planners are all correct, and what's mysterious is why there is such a difference in efficiency, and how the math adds up to get to 249/265 rated miles for the two models.

    upload_2017-6-1_12-27-27.png
     

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  17. schwedisch

    schwedisch Member

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    No, EVTripPlanner gives different numbers for 75D and 75, the 75D is more efficient than the 75, but not as huge a difference as between the S85 and S75.
     
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  18. David99

    David99 Active Member

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    Ah OK, so that's eliminated. I just can't see how the 75 would be that much more efficient.

    Back to the original question, I believe the 85 has a higher voltage battery so Supercharging might be faster.
     
  19. whttiger25

    whttiger25 Member

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    I'm curious, how much rated range do your two vehicles display on a 100% charge?
     
  20. Jeeps17

    Jeeps17 Cath Jockey in a P85

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    I would not be surprised if the S75 was lighter that the older S85, given the continuous improvements made on the vehicle design over the years.

    I doubt that this is enough to account for such a discrepancy, but it may contribute.
     

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