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.23Cd ?

Discussion in 'Model 3' started by TEG, Jul 29, 2017.

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  1. McRat

    McRat Active Member

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    No 32 is right, but my unit analysis sure sucks.

    ~14.9 kW to stabilize at 65 mph would yield 253 miles of range using 58 kWh. This is probably close with no AC.
    ~22.0 kW using the same variables at 75 mph would yield 197 miles. This is probably close with no AC.

    But then why is the difference 32.2%... Owww... You cover more Miles Per Hour at the higher speed. So the real difference is 17.2% more losses PER MILE. Dumb mistake.

    But still, the Bolt should not be so much more efficient of the Volt at highway speeds due the huge difference in aero drag. That's a lot of waste heat being spewed by the EV system in the Volt.
     
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  2. Jeff N

    Jeff N Active Member

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    Ah, that makes sense. I confused myself by referring to power instead of energy.
     
  3. ikjadoon

    ikjadoon Member

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    Did anybody ever explain these Consumer Report results vs. EPA ratings? I think Chevy should've been sucker-punched in their range with 65mph testing vs a Tesla Model S, but apparently it overperformed its EPA rating.

    CR EV range test methodology:
    Cabin heating/cooling is turned OFF
    Primarily 65mph constant speed

    Model S 75D: 235 miles (9.2% lower than Tesla/EPA-rated range)
    Model X 90D: 230 miles (10.5% lower than Tesla/EPA-rated range)
    Chevy Bolt: 250 miles (5.0% higher than Chevy/EPA-rated range)

    Really? I'm not talking about the two cars absolute range, but the deviations from their factory/EPA range. Shouldn't a test that's predominantly at highway speeds have much lower range than the EPA's average ~45mph testing? Tesla's results make sense; at highway speeds, it will have less range than at the EPA test speeds. Chevy's don't.
     
  4. SageBrush

    SageBrush Active Member

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    The EPA test is on a dyno indoors, and combines the 2 cycles of city and highway. An average speed is a very loose and inaccurate representation of the actual test.

    That said, I think I remember @Jeff N saying that other outside runs of the Bolt at 70 mph returned 190 miles. Perhaps the CR test was done with a tail-wind.
     
  5. Jeff N

    Jeff N Active Member

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    No, that was Car & Driver's test which got 190 miles at 75 mph with the A/C set to 72F. I have roughly confirmed it during my own drive at an average of 74 mph for around 100 miles in the Central Valley recently.

    As I noted on another thread here, these EPA and CR estimates are combined city/highway numbers. CR has a reputation for being tough on the city portion (vs EPA) presumably due to harsh braking stops and strong starts and easy on the highway portion (vs EPA) by mostly driving steady state at 65 mph.

    Thus, the Bolt does well with its strong regen on the brake pedal where Tesla only does friction braking plus some regen from taking the foot off the accelerator. The Bolt is also probably designed to have a motor efficiency sweet spot around 65 mph whereas the Tesla cars cited are probably designed around acceleration performance (the Model 3 might be tuned differently).
     
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  6. SageBrush

    SageBrush Active Member

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    #26 SageBrush, Aug 5, 2017
    Last edited: Aug 5, 2017
    Thanks for the correction. The higher speed works out to less than 20% greater energy consumption* in the Bolt, so the CR highway result of 250 miles at 65 mph still does not come close to lining up with 190 miles at 75 mph. I ignored the A/C though.

    If you and C&D are correct, then 65 mph should give a range of about 228 miles, or about 5% less than the combo EPA range of 238 miles.

    *About 52 Wh/mile more aero at the higher speed
     
  7. Jeff N

    Jeff N Active Member

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    My impression is that 228 milesis easy to achieve at 65 mph with A/C off -- maybe significantly more.
     
  8. SageBrush

    SageBrush Active Member

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    Does your Bolt have CC ?
    Take it for a spin ! 15 miles each way should do it.
     
  9. stopcrazypp

    stopcrazypp Well-Known Member

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    Actually Tesla's results don't make sense, from my impressions all these years on TMC, travelling at 65mph steady state should be perfect to achieve EPA range.

    And you can see from the S85, that it matches EPA range of 265 miles at roughly 65mph.

    [​IMG]
    Model S Efficiency and Range

    I would say either CR did not charge the car fully (a distinct possibility given how both numbers are very close to the standard charge mode), there is extra degradation on their batteries (both Tesla's are 2016 models, while Bolt is brand new), the batteries are out of balance (if they rarely fully charge the cars), or there is a significant amount of city cycle in the test that they glossed over.

    You can't generally say a test at higher steady speeds than EPA would have much lower range. To illustrate this, you can take a look at the EPA test ratings (MPG):
    2016 S 75D 103 combined, 102 city, 105 highway
    2016 X 90D 92 combined, 90 city, 94 highway
    2017 Bolt 119 combined, 128 city, 110 highway

    Note for all the Teslas the city cycle test (which is a lot slower average speed) is worse than the highway cycle. The Bolt is the exact opposite.

    The EPA tests (even the highway ones) have a lot of acceleration/deceleration/start/stop cycles which do not favor a heavier car like the Teslas running on wide sport tires (vs the narrower LRR tires on the Bolt).
     
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  10. Jeff N

    Jeff N Active Member

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    #30 Jeff N, Aug 5, 2017
    Last edited: Aug 5, 2017
    I think that's the main explanation. Like the EPA combined estimate, CR's number probably has close to 50% city estimate mixed into it.

    For example, for the 2017 city estimate:

    Make/ Model EPA CR
    Toyota Prius 54 43
    Toyota Prius C 48 37
    Tesla S P90D 102 64
    Chevy Bolt EV 128 128*

    *Although the numbers published on consumerreports.com exactly mirror EPA for Bolt so perhaps they haven't been updated correctly.

    This is true even though the Prius has some regenerative braking on the pedal (although only ~25 kW and not ~60 kW like the Bolt) and are relatively light weight cars.

    Im guessing that even if the Bolt gets a real city CR estimate below 128 that it's reduction ratio from EPA is much less than Tesla's nosedive from 102 MPGe EPA to 64.
     
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  11. stopcrazypp

    stopcrazypp Well-Known Member

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    I think you are right. I looked at the source article more closely, and it says this:
    "CR’s electric-vehicle range test involves some mixed driving, but much of it is done by driving a constant 65 mph on a highway."
    Chevrolet Bolt Sets Consumer Reports' Electric-Vehicle Range Record

    Then I look at the link they gave on how they do their test in general, and as you mentioned, it seems this is CR's version of the EPA combined cycle:
    "Fuel Economy
    We perform our own fuel-economy tests, independent of the government's often-quoted EPA figures and the manufacturers' claims. Using a precise fuel-flow measuring device spliced into the fuel line, we run two separate circuits. One is on a public highway at a steady 65 mph. That course is run in both directions to counteract any terrain and wind effects. A second is a simulated urban/suburban-driving test done at our track. It consists of predetermined acceleration, and deceleration rates, as well as idle time. Consumer Reports' overall fuel-economy numbers are derived from those fuel consumption tests."
    How Consumer Reports Tests Cars

    So the characterizations from the other articles (which seems to be based more the video, which does not mention city testing) are extremely misleading as they all present this result as simulating the steady state 65mph, when in fact, it's a mixed cycle.
     
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  12. bro1999

    bro1999 Member

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    Would be good to dig up how other EVs did on CR's range test compared to their EPA ratings. Did CR ever test the Leaf, i3, Soul EV, etc...?
     
  13. techmaven

    techmaven Active Member

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    The CR’s Model S 75D got something in the neighborhood of 315 Wh/mile. That’s really high for some mixed driving, much of it at 65 mph in the highway. On the older, less efficient 85’s, I would expect under 300 Wh/mi with one driver, no passengers, and no HVAC. It is very suspicious.

    All it would take is extra usage of the accelerator and don’t allow the car to regen sufficiently during the “mixed” portion. They also don’t really tell us just how much of it was at 65 mph. It also doesn’t match up with Idaho National Labs AVT testing of a 2014 S85:

    https://avt.inl.gov/sites/default/files/pdf/fsev/fact4500tesla2014.pdf

    The DC electricity consumption rate (pull from battery while driving) was 301 Wh/mi at 70 mph. At 60 mph, it’s a mere 245 Wh/mi. That’s with the older drive unit and heavier battery pack. CR tested with a 75D which has two of the newer, or efficient drive units. It should be at least 10% more efficient. At a steady 70 mph, I would expect the 75D to achieve 250 miles. So not really sure what CR did, but one of the biggest issues may be having humans drive a course without controlling for acceleration and deceleration profiles. The EPA testing is pretty strict about the acceleration and deceleration and the resulting speeds throughout the test. Unclear if CR is that rigorous.
     
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  14. stopcrazypp

    stopcrazypp Well-Known Member

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    #34 stopcrazypp, Aug 5, 2017
    Last edited: Aug 6, 2017
    They say that the test does control for acceleration and deceleration rates, but it appears to be done using mph markers.
    "The city test is conducted on a loop that’s set up on our track to reflect driving in a suburban area. It’s marked so that a driver must maintain specific speeds in certain sections and stop the car at specific points for set idling times. Highway mpg is measured by driving on a particular stretch of sparsely used freeway near our test track at a steady pace of 65 mph. Each driver runs the test in both directions to compensate for wind and the slight difference in grade."
    The Miles per Gallon Gap - Consumer Reports Magazine

    Depending on how tight or loose these are, it may affect how much and if any regen is done. With how they characterize the EPA test (saying the acceleration rates are too low), I would guess it errs on the side of tight. Given this is done by a human, I would say this would favor brake blended regen and against accelerator based regen that Tesla uses because having to decelerate according to specific speed markers is probably harder to do without using brakes. The driver might not even do some initial deceleration with regen, but rather just go directly to brakes at the specified point.

    Similarly there is some leeway in accelerator usage too.

    @Jeff N posted a sample of the P90D which is rated 64 MPGe under CR's city cycle vs 102 MPGe on EPA city, so the city test does skew very poor for Teslas (probably what you mentioned, extra acceleration and less chance for regen).
     
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  15. stopcrazypp

    stopcrazypp Well-Known Member

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    To bring this back on topic,

    The sticker for the Model 3 (310 mile version given that is what is being delivered) seems to show 126 MPGe, making it the second most efficient EV behind the Ioniq at 136 MPGe.
    This is a pleasant surprise for me, since I didn't expect it to beat the i3 at 124 MPGe.
    https://photos.google.com/share/AF1QipP3fdPAC7K_4U4gNR0VjFUbG1cfM7SwTbV8-Q9zF1nktmkljtnRKSdw6CCxVTauXw?key=TGZwWFhSR0NSSWRXQW5sRFp5N0h6ZGVKeHZMSGdB
    Hyundai Ioniq Electric becomes most efficient electric car ever rated by the EPA

    Unfortunately the picture is too low resolution to show much else.
     
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  16. techmaven

    techmaven Active Member

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    This is the LR version too... the standard version should be even higher.
     
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  17. ikjadoon

    ikjadoon Member

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    The EPA dyno test apparently takes into account wind resistance (do they take the cars to a wind tunnel??) and the vehicle weight. Still, they should both err on the same side. Either the EPA testing is too conservative or too demanding. Very true: average speed is a bad summary: the acceleration and braking matter, too.

    Right, that's the Car & Driver test:



    But unlike the EPA (4/5 tests are without HVAC) & Consumer Reports, C&D had HVAC on and nothing to account for wind; their results are a tad suspect (as I would say if they tested a Tesla that way, too).

    (EDIT: Ninja'd by @JeffK himself!)

    Thanks for the link and graph; it does line up perfectly.

    1. Charge level: true. This would be quite a silly mistake as they've owned the Tesla's for a while.
    2. Battery degradation: also true. It depends on how far they've been driven; 40k km would be roughly 96.5% of the original capacity.
    3. City cycle being included: right. The Chevy Bolt is 128/110, S 75D is 102/105, and X 95D is 91/95. EPA's combined seems close to 50% / 50% weighting (if not exactly).

    Agreed; seemingly all five of EPA cycles seem worse for Tesla...but a test of "much" of 65mph should've favoured the Tesla then, right? I would love to see CR's actual velocity over time graph here, like the EPA offers.

    But I'm curious. CR specifically calls it their "electric vehicle range test"--are they using the same methodology as for their ICE cars? I would imagine it's a 50/50 split between their two ICE tests and then it's crazy to call "much" of it at 65mph. I want to say it's a different, primarily highway test.

    So---here are the thoughts I see:

    1. Tesla does worse in city vs highway. The EPA testing, even highway, leans toward slower city driving. Maybe the CR test skews even heavier towards cities, so EVs with higher EPA city ratings would exceed their estimates and EVs with lower EPA city ratings would feel the brunt. However, this conclusion would turn CR's "much at 65mph" claim into fiction. Maybe they're being imprecise with their words.

    2. They screwed up the charging or battery degradation has taken its toll.

    3. CR used real drivers (instead of the dynos as used by the EPA), introducing human error (excess acceleration; inconsistent use of regen).
     
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  18. stopcrazypp

    stopcrazypp Well-Known Member

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    A lot is discussed here already, if the results from the P90D is any indication, Tesla does horrible in the CR city test (only 62.7% of EPA city rating)
    .23Cd ?

    As for the "much" terminology, having half or even more of the cycle being city cycle still matches it. CR did not say "a majority at 65mph" or "almost all at 65mph". 50% at 65mph is still much, as is 45% (if they follow EPA). The video was more misleading as it didn't mention mixed driving at all.
     
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  19. Topher

    Topher Energy Curmudgeon

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    How useless is it to tell us the temperature that the AC is set at? Temperature difference is what matters.

    Thank you kindly.
     
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  20. bro1999

    bro1999 Member

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    They should have simply left the A/C OFF, as a setting of 72 when it's 100 degrees out uses a bit more energy than 72 when it's 72 out.
     
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