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60KW More Efficient???

Discussion in 'Model S: Battery & Charging' started by johnmodels, Sep 1, 2013.

  1. johnmodels

    johnmodels Member

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    Hi All!

    So I had a 60KW loaner the other day and enjoyed comparing the differences between a newer production (15XXX) 60kw to my slightly older s85 (60xx). One thing I found interesting is that the 60 was getting far better w/mi. than my s85.

    I take the same route and know what my numbers pretty well since I have put over 10,000 miles on my 85. I can say conclusively, where my s85 would average about 350 w/mi the 60kw would average about 315 w/mi. Even when driving the 60 harder than I would the 85, cuz it's a loaner, I could not get the 60 over 320 w/mi.

    I have a lifetime average of 349 w/mi on the s85 and it is my guess that I would average about 310 w/mi on the 60.

    The 60 had 19" wheels, pano roof, and thats it. No tech, no fog lights, etc.
    My s85 has 20" staggered wheels (8.5 front, 9.5 rear) loaded.

    I'm thinking the wheels are some of the difference, but the weight and limited power output of the 60 might be the rest.

    Thats a pretty big difference! About 10%+.

    FWIW, The 60 felt a bit lighter, which it is of course, and quick, but it lacked the more neck snapping acceleration that my s85 has.

    Any thoughts???

    John
     
  2. dirkhh

    dirkhh Middle-aged Member

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    The 21" wheels alone are said to add 6% to the consumption. Not sure about your staggered 20" ones. The rated miles for the P85 appear to be based on 318Wh (IIRC), for the S60 it's 298.
     
  3. stephenpace

    stephenpace VIN S00219

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    What @dirkhh said. Mounted 19" tires weigh less than the 21", plus the 21" tires have more rolling resistance (20" probably similar). You might also check to see if you are carrying something in your car that weighs enough to affect mileage. For instance, the rear car seats probably add a bit.
     
  4. Jeff Miller

    Jeff Miller Member

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    Your observation is consistent with average mileages over many drivers for the two vehicles - see bold below.
    This lends more weight to the idea that some of the differences in mileage is from the car specs (battery, wheels) rather than the driver.
    (The pure CA numbers are not far off either). See the lifetime wh/mi thread for details.

    Battery Wheels Wh N Miles stdev
    1 40 19 270 2 6300 5
    2 60 19 312 27 95937 24
    3 85 19 341 49 271346 36
    4 85 21 356 44 232483 35
     
  5. brianman

    brianman Burrito Founder

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    Nitpick in the title and OP: 60 kWh

    The nitpick actually matters here because part of this discussion that's missing is the difference in the acceleration cap in the UI: 240 kW vs. 320 kW. We know from REST data that both vehicles can deliver somewhat above the UI cap, but I don't think you can get a 60 kWh above 300 kW but you can do it at just about every red light on in the 85 kWh if you want to.

    The "ready availability" and "easy of application" of power in the Model S generally makes it easy to intentionally or accidentally consume as much power as it will let you, so that cap matters when comparing the vehicles. It's quite different than an ICE where the churning through gears gives you plenty of cues that you're using more.

    - - - Updated - - -

    If you want to do a more scientific comparison, go for a test drive with a friend on not-very-busy road that has at least two lanes in each direction. Pick a speed and put the vehicles side-by-side with cruise control set to the same speed. If the vehicles hold position next to each other, then you'll have a valid test. If they don't, then you have to get that fixed first. Connect to each other over Bluetooth phones to chat while you drive. Alternate calling out power consumption from the right-arc of the speedometer display every 10 seconds or so. After 5 miles, come to a complete stop by releasing cruise control and having whichever vehicle stops more quickly pull in behind the other so that you can both safely park on the shoulder with your hazards on. Take pictures of whatever in-car display you want (5 mi energy, trip meter, etc.).

    Bonus points: Have your home computer be running REST for each vehicle so that you can compare somewhat-official-from-car telemetry later.

    Make sure the vehicles have the same wheel sizes (19 / 21) and neither of them has anything differentiating like aero wheels, cyclone wheels, aftermarket wheels, or plus package going on. Technically they should be identical with respect to having panoramic roof or not. Etc.

    Even with all that you may still have issue getting a viable comparison due to external factors like wind and inconsistent unevenness of the road across the two lanes, and potholes, and ....
     
  6. cinergi

    cinergi Active Member

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    The 85 is rated for 89 MPGe and the 60 is rated for 95 MPGe, so, all other things being equal -- yes, it's supposedly more efficient.
     
  7. brianman

    brianman Burrito Founder

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    That includes from-wall effects though, IIRC. Also we don't know the configurations of 85 and 60 they tested.
     
  8. SFOTurtle

    SFOTurtle Active Member

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    I assumed from the title that the OP was inquiring as to whether the car itself, 60 v 85, was more efficient as opposed to the battery cells/chemistry of the battery pack itself. If the 60 car as a whole is a few hundred pounds lighter than the 85 car as a whole, wouldn't it stand to reason that the wh/mile would be less on the 60 car than for the 85 car? Maybe I'm missing something here?
     
  9. stopcrazypp

    stopcrazypp Well-Known Member

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    Brian is saying the 89MPGe and 95MPGe numbers includes charging losses (independent of the battery-to-wheel Wh/mile number you see in your car). If the 60kWh and 85kWh cars tested on the EPA cycle had different chargers, then it's not clear if the difference in efficiency is from the charging equipment or battery-to-wheel or both.

    Of course the difference in weight, wheel size, tires, etc. will play a role in the battery-to-wheel number.
     
  10. jerry33

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

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    Just the difference in tires can easily be 10%. To get the actual number you either have to have a large number of cars all reporting (where the amount of cars makes up for the individual variances) or a few highly controlled test runs. However, I don't doubt that the 60 kWh will be more efficient because it's lighter.
     
  11. SFOTurtle

    SFOTurtle Active Member

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    Right, then I had interpreted the OP's question differently. Either way, I learned something from this thread.
     
  12. brianman

    brianman Burrito Founder

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    At a high level, I think it's easy to say that 60 kWh drivers will generally experience better efficiency but I think a significant factor in that is that the 85 kWh car "lets" you spend more every time you accelerate.

    Put another way, a driver like jerry33* could probably get comparable numbers between 60 and 85 if other vehicle variations (wheels, chargers, etc.) were neutralized.

    * To be as clear as possible, this is a compliment to his skills and willpower.
     
  13. Dreamin

    Dreamin Member

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    I'm going to say it's your car's aggressive wheel setup accounting for most of this 10%. From the SAE article on the car's aerodynamics, it states that wheels generate 20% of the total drag on the vehicle - likely why the factory wheels have such an 'inboard' offset... not the best for aggressive aesthetics, but great for efficiency. A more 'outboard' offset and wider wheels will impact efficiency.
     
  14. Chas F

    Chas F Model S 60kWh #P6396

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    I didn't think weight was a factor. While the MS 60 has less "operational" batteries, I was always led to believe that both the 85 and 60 weighed the same. No? Allowed them to saftety test only one model?
     
  15. jerry33

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

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    No. There's a thread with the weights and the 60 weighs less.
     
  16. Jeff Miller

    Jeff Miller Member

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    One of the biases in the wh/mile thread is that the 85s came out before the 60s. So the 85 data includes more winter driving.
    (Over time, as we collect more data, this bias will disappear).
    As a sort of fast and loose way to reduce this bias, I looked at the data for people who started reporting after the middle of May.
    Surprisingly, at least in this set, there doesn't seem to be much of a wheel effect. The 21" 85s and the 19" 85s have basically the same
    mileage. The 19" 60s however are about 10% more efficient than the 19" 85s.

    Battery Wheels Wh N Miles stdev
    1 40 19 270 2 6300 5
    2 60 19 307 14 49412 20
    3 85 19 330 17 97993 35
    4 60 21 294 1 2363 NA
    5 85 21 336 11 46421 34

    If I further restrict the set to people who started reporting after Mid May and have less than 5k miles (trying in a crude way
    to eliminate people who have had their car since winter but started reporting recently) I see something similar - battery size seems to matter much more than wheel size. These are small data sets (I encourage everyone to report their wh/mile on the wh/mile thread so we can get better stats), so the results are far from definitive, but it's nonetheless interesting.

    Battery Wheels Wh N Miles stdev
    1 40 19 270 2 6300 5
    2 60 19 305 11 28348 21
    3 85 19 322 9 26067 37
    4 60 21 294 1 2363 NA
    5 85 21 324 8 19838 22

     
  17. brianman

    brianman Burrito Founder

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    Interesting, Jeff.
     
  18. David_Cary

    David_Cary Member

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    Does that analysis take into account that people who pick 21 inch rims would tend to live in the warm areas of the country. I can't imagine driving around Manhattan (as an extreme example) in 21s but here in NC, I can easily imagine it. Then you have different average speeds as TX has 85 mph and lots of NY (?all) have 55 mph.

    With such a small data set, it is easy for something like region preference to sneak in.

    When the 60 got tested, I personally thought the numbers were shockingly better and didn't really understand it. Now invertors can vary in efficiency and it is possible that the invertor for the 60 is more efficient. I highly doubt that the better acceleration of the 85 alone would affect EPA numbers. I also doubt that it would effect real life numbers that much since accelerating to 60 in 4 secs uses only a tiny bit more energy than getting there in 6 secs with an EV - sure there is a tiny bit of extra heat generated but it is probably in the 1% range.
     
  19. mknox

    mknox Well-Known Member

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    Huh? I thought the loaners were supposed to be top-of-the-line fully loaded cars???
     
  20. darthvdr

    darthvdr Member

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    Very interesting. Thank you for sharing. I do wonder, if the P85s typically have more accessories and options added that weigh the car down more.
     

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