AWD and Performance EPA range certification

jsmay311

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#1
I am sure it has been talked about somewhere but I can’t find it. There has to be a reason for the induction motor in the front of the AWD. It is not efficiency.
Based on the first nugget of AWD efficiency information, you sure got that one right:

https://teslamotorsclub.com/tmc/threads/model-3-awd-performance-lower-udds-range.122140/

[mod edit: here are direct links to the CARB documents]
https://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2018/tesla_pc_a3740023_0_z_e.pdf
https://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2018/tesla_pc_a3740022_0_z_e.pdf
 
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Bokonon

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#2
FYI, per InsideEVs and this TMC thread --

CARB has published their UDDS (Urban Dynamometer Driving Schedule) certification for the Performance and AWD variants of the Model 3:

https://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2018/tesla_pc_a3740023_0_z_e.pdf

This test cycle seems to simulate spirited city driving with a lot of acceleration and deceleration. Here's a plot of the speeds used during the cycle:

Both Performance AWD and regular AWD were certified at 455.32 miles AER (all-electric range), which is about 8% less than the Model 3 LR with RWD. For reference, here's where these test results fall within the context of the Tesla sedan family:

Model 3 LR: 495.1
Model 3 LRD: 455.32
Model 3 P: 455.32

Model S 100D: 449.7
Model S P100D: 414.4
Model S 75D: 345.6
Model S 75: 333.4

Keep in mind that the highway test results are still unknown at this point, so it's possible that, much like the Model S 75D vs. 75, the AWD variants of the Model 3 will perform better on the highway tests than their RWD counterpart. But it seems like that outperformance would have to be significant in order to keep pace with the Model 3 LR in terms of overall rating.

(Question for the first-principles folks here: could the weight of the front motor assembly alone account for the 8% difference in range in this particular test cycle, with its focus on constant acceleration and deceleration from/to a stop?)

On the plus side, getting CARB-certified is one fewer regulatory hurdles that Tesla has left to clear before it is able to begin P / AWD deliveries. (What say you, EPA?) :)
 
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Eigenv1

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#3
FYI, per InsideEVs and this TMC thread --

CARB has published their UDDS (Urban Dynamometer Driving Schedule) certification for the Performance and AWD variants of the Model 3:

https://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2018/tesla_pc_a3740023_0_z_e.pdf

Model 3 LR: 495.1
Model 3 LRD: 455.32
Model 3 P: 455.32

Model S 100D: 449.7
Model S P100D: 414.4
Model S 75D: 345.6
Model S 75: 333.4

Keep in mind that the highway test results are still unknown at this point, so it's possible that, much like the Model S 75D vs. 75, the AWD variants of the Model 3 will perform better on the highway tests than their RWD counterpart. But it seems like that outperformance would have to be significant in order to keep pace with the Model 3 LR in terms of overall rating.
Thanks for posting this. I find it curious that the all wheel drive and faster all wheel drive performance version have exactly the same CARB rating. The decrease in the rating may account for the reason why the 20 inch tire performance version is listed as an option as opposed to a separate model.
 

Petra

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#4
This test cycle seems to simulate spirited city driving with a lot of acceleration and braking. Here's a plot of the speeds used during the cycle:
Ahhahahahahahahahahahahahahaha *gasps* hahahahahaha...

There's nothing spirited about the UDDS. Look at the x-axis, look at how long the car is taking to accelerate to 20-30mph. Sure, the graph looks spikey but that's because the full 1400 second test period is shown in that chart.
 

Bokonon

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#5
Thanks for posting this. I find it curious that the all wheel drive and faster all wheel drive performance version have exactly the same CARB rating. The decrease in the rating may account for the reason why the 20 inch tire performance version is listed as an option as opposed to a separate model.
Yeah, I'm wondering whether they only tested one variant (an already-built P?) and were able to assign the same results to standard AWD by virtue of the drivetrain being sufficiently similar. (The EPA allows this sort of thing, almost to an egregious level -- e.g. when Ford tested the aerodynamic Fusion Hybrid at 47 mpg and then assigned the same EPA rating to the boxy CMax Hybrid.) Which begs the question you're asking: which specific configuration was tested, and how well does its performance translate to other AWD configurations?
 

Bokonon

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#6
Ahhahahahahahahahahahahahahaha *gasps* hahahahahaha...

There's nothing spirited about the UDDS. Look at the x-axis, look at how long the car is taking to accelerate to 20-30mph. Sure, the graph looks spikey but that's because the full 1400 second test period is shown in that chart.
Stricken from the record, your honor. :)

Aaaand that's my cue that it's bedtime.
 

garsh

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#7
Based on the first nugget of AWD efficiency information, you sure got that one right
For those who want a direct link, here are CARB certification documents for Model 3 AWD and Performance.
TLDR: Tested range was 455 miles versus 495 miles for First Production.

https://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2018/tesla_pc_a3740023_0_z_e.pdf
https://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2018/tesla_pc_a3740022_0_z_e.pdf

And an article on InsideEVs:
BREAKING – Tesla Model 3 AWD & Performance Rated With 455-Mile Range By CARB

Note that this is the city portion (UDDS) of the test. There's still a chance that the dual-motor will perform better than the single motor car on the highway test (HFEDS). The RWD car got 455 on that test.

Previous thread on Model 3 Long Range certification
 
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garsh

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#8
Furthermore, the normal "fudge factor" procedure for deriving EPA city range from this value is:

City Range = 455 * .7 = 318 miles
Then of course, Tesla is permitted to advertise a lower number if they want. And I believe they've already decided to stick with the 310 mile range already advertised for the RWD 3.
 

KarenRei

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#9
If it is a weight issue, it'll have a much more profound impact on city driving vs. highway.

I don't know the details of the drivecycle to know if it should have ever forced the (less efficient) front motor on. Aka, whether the cycle has the vehicle accelerate to a given speed "as fast as it can" (which will vary between vehicles), or at a given constant rate. If it's purely a weight issue, that'd imply that the AWD version is 138kg (305 lbs) heavier, which sounds rather high.

Like most people, highway range is all I care about. Unless you're working as a taxi driver of an in-town courier, you'll never exhaust that sort of range in city driving.
 

Brokedoc

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#10
I don’t know anything about this test so correct me if I’m wrong but isn’t this test performed on a Dynamometer? UDDS (Urban Dynamometer Driving Schedule)

If so, vehicle weight and aerodynamics are not a factor because the car is stationary.

The calculated range would purely reflect the efficiency of the powertrain and capacity of the battery?
 

garsh

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#11
I don’t know anything about this test so correct me if I’m wrong but isn’t this test performed on a Dynamometer? UDDS (Urban Dynamometer Driving Schedule)
Yes, it is.
If so, vehicle weight and aerodynamics are not a factor because the car is stationary.
No, that is incorrect. :)

We already hashed out all of this stuff in the old EPA Certification Data thread. I suggest reading through that thread - there's a lot of good information we discovered, uncovered, and figured out about this whole testing process.

The dyno test scores are unrealistically high for all EVs and they need a multiplier to convert them to realistic range numbers. Initially, I also assumed the reason they were so high must be the missing air drag but then I did more research and it appears air drag is included. The way they include the air drag is by letting the car coast on actual roads and they measure how much it drives while coasting from around 75 mph to 10 mph. Then they set the dyno settings so that it coasts the same distance on the dyno.
 

Brokedoc

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#12
We already hashed out all of this stuff in the old EPA Certification Data thread. I suggest reading through that thread - there's a lot of good information we discovered, uncovered, and figured out about this whole testing process.
Interesting that the dyno is programmed to drag at an rate equivalent to average aerodynamic resistance/inertia/rolling resistance. Hopefully the algorithm is complex enough to be able to adjust the drag at different speeds since the wind resistance changes exponentially.

What about the benefit of regen? Does the testing criteria take that into account? AFAIK, dynos are passive and do not simulate vehicle momentum to feed regen into the wheels.
 

garsh

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#13
Interesting that the dyno is programmed to drag at an rate equivalent to average aerodynamic resistance/inertia/rolling resistance. Hopefully the algorithm is complex enough to be able to adjust the drag at different speeds since the wind resistance changes exponentially.
Technically, it varies with the square of speed, not exponentially.

Jalopnik actually has a pretty good overview article on this subject. The dyno lets you enter three coefficients.

How Fuel Economy Is Measured (And Why You Get Different MPGs)

And the relevant section:


This is a second order polynomial, which makes sense, since aerodynamic drag varies with velocity squared. The coefficients in this equation are called “Coast Down Coefficients” or “ABC Coefficients.” An easy way to understand this formula is to think of the C term as representing aero drag, while the B and A term roughly represent drivetrain losses and rolling resistance, respectively.​

What about the benefit of regen? Does the testing criteria take that into account? AFAIK, dynos are passive and do not simulate vehicle momentum to feed regen into the wheels.
It's up to the driver to make use of regen instead of the brakes as appropriate whenever it's time to slow down within a test cycle.
 
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#15
Thanks for posting this. I find it curious that the all wheel drive and faster all wheel drive performance version have exactly the same CARB rating. The decrease in the rating may account for the reason why the 20 inch tire performance version is listed as an option as opposed to a separate model.
I agree they chose to make the 18” Aeros stock to hit their range targets. Interestingly, the EPA requires optional equipment to be included if the connect rate is above a certain percentage. I believe it is 60%. According to @Troy ‘s spreadsheet, the connect rate for the AWD-P Powertrain is above 57% (57/99 P confirmations include the 20” wheels). I wonder if they will have to re-certify and revise the range down if the 20” wheel connect rate increases?
 

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#17
Yes, please! Comparative data in the same conditions vs. a RWD on the same wheels/tires, same pressure, driving the same road in a loop, at different speeds!
 

John

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#19
I have found Troy's speed/range table to work out to within 1% of what I'm getting in my LR RWD 19". He thinks the car should be advertised as getting 297 miles of range. I get 294 miles.

FWIW, I am guessing that table will work just as well for AWD, since it's based on EPA dyno results, and the aerodynamics are calibrated by other configs.
 

KarenRei

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#20
I have found Troy's speed/range table to work out to within 1% of what I'm getting in my LR RWD 19". He thinks the car should be advertised as getting 297 miles of range. I get 294 miles.

FWIW, I am guessing that table will work just as well for AWD, since it's based on EPA dyno results, and the aerodynamics are calibrated by other configs.
You up for doing some head-to-head driving tests (same place, same time, both directions) up against a AWD in the same config (particularly tires)? That's what we really need: someone with AWD and someone with RWD, in the same config, driving at the same speed, in the same conditions.
 
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