It's alive! [All spoiler, no speculation]

[EvanLin]

So what is the significance of the RLHP @ 50 mph (Road Load Horsepower) values?
The EPA document lists values for the 2 wheel configurations.
18" - 9.95
19" - 11.13
So the 19" is 11.8% more than the 18"
Does anybody know how these values would effect rated range for a car with 19" rims?
I'm assuming its more complicated than just saying the 19" rims would be rated at 277 miles, but maybe not?

"Road Load HP" should mean the drag from the road via tires.
It's just a parameter (to simulate real world road drag) in the MPG testing machine I suppose.

Road drag accounts for ~1/4 of total drag @ 50mph.
Therefore, the 11.8%(~12%) difference between 18" & 19" wheels equals to 3% of total range difference. Reasonable.

 

[T34ME]

"Road Load HP" should mean the drag from the road via tires.
It's just a parameter (to simulate real world road drag) in the MPG testing machine I suppose.

Road drag accounts for ~1/4 of total drag @ 50mph.
Therefore, the 11.8%(~12%) difference between 18" & 19" wheels equals to 3% of total range difference. Reasonable.

Throw an additional ~3% for using the aero wheel covers and I am right there with you.

 

[scottf200]

Are those mid-size though? seem to be in the compact category

On the right side under 'My Selections' click the modify button to pick he offered classes.

Link to what I was viewing: Fuel Economy

 

[Zoomit]

"Road Load HP" should mean the drag from the road via tires.
It's just a parameter (to simulate real world road drag) in the MPG testing machine I suppose.

Road drag accounts for ~1/4 of total drag @ 50mph.
Therefore, the 11.8%(~12%) difference between 18" & 19" wheels equals to 3% of total range difference. Reasonable.

No, the road load HP and the A, B, C terms are dynamometer power absorber settings. They are calculated to calibrate the test dyno and replicates "tire rolling resistance, driveline losses, and aerodynamic drag." https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=34102&flag=1

The range difference between Aero and Sport wheels is 10%, which was indicated previously by the Tesla VP of Engineering: Tesla Model 3 aero wheels can increase efficiency by ~10%, says VP of Engineering

Note: This difference is a combination of rolling resistance and aerodynamic drag. The rolling resistance is primarily a function of tire compound and the aero drag is a function of wheel design (aero cap) and tire/wheel width.

 

[FlyingKiwi]

Now I want to see the same test done with the 18" wheels, once with covers on, and once with covers off, to see how much is down to the covers, and how much is wheel/tyre. Actually just the ABC coefficients should be enough.

 

[stopcrazypp]

Battery Specifc Energy, Wh/Kg 150
Total Battery Weight, Kg 480

So 72 kWhs

Given how round the number is, I suspect one of these is not correct or that they don't refer to the same "battery" parts (some parts are not included in the other).

From the same report:
"Range Test Results
Vehicle ID 3R217‐R00012
Transmission AV/1
ETW 4250 (4126 ‐4375)
RLHP 9.95 @ 50 MPH

City Range, miles 495.04
System AC, Wh/mile 180.6035876
System DC, Wh/mile 165.31
Vehicle DC, Wh/mile 158.11

Highway Range, miles 454.75
System AC, Wh/mile 196.6047279
System DC, Wh/mile 179.96
Vehicle DC, Wh/mile 172.12"

This implies city DC consumption was 495.04*158.11 = 78.271 kWh
Highway DC consumption was 454.75 * 172.12 = 78.272 kWh

So it's impossible for the battery to only be 72kWh.

 

[SageBrush]

My money's on the five cycle test.

For what ?

I'm interested in range at 65, 70 and 75 mph cruising. I think that 70% of the raw highway result is a pretty good surrogate for 65 mph cruising, so that works out to 454*0.7 = 317 miles and therefore 78000/317 = 246 Wh/mile. The additional Wh/mile from higher speeds is easy enough to calculate ... or to just look up in my SS:

Newtons of Aero at
266, 65 mph -> 74 Wh/km
308, 70 mph -> 85.5 Wh/km
353, 75 mph -> 98 Wh/km

So taking the difference ...
70 mph is 11 Wh/km more
75 mph is 24 Wh/km more

Using 1.61 Km to a mile,
70 mph has 18 Wh/mile more consumption than 65 mph
75 mph has 38.64 Wh/mile consumption than 65 mph

Added all together,
70 mph is 246+18 = 264 Wh/mile and range is 78000/264 = 295 miles
75 mph is 246+38.64 = 284.64 wh/mile and range is 78000/284.64 = 274 miles

 

[dhanson865]

It does however show something I didn't expect.. ignoring the left hand side of the graph and the missing power consumption (which should be the same for either wheel/tyre selection).. I would have expected as speed increased the benefit of the aero wheel increased since the aerodynamic drag becomes more and more dominant with increasing speed, so the difference between the 18s and 19s should increase, but that graph doesn't appear to show it. it seems to be more constant or maybe even slightly declining.

The test was on a dyno, think of it as a stationary treadmill for cars. There is no aero in the test results because they are synthetic.

For gas cars they put a big fan in front of the car to keep the engine from overheating. For an EV they wouldn't bother.

 

[dhanson865]

Now I want to see the same test done with the 18" wheels, once with covers on, and once with covers off, to see how much is down to the covers, and how much is wheel/tyre. Actually just the ABC coefficients should be enough.

For that you'll have to deal with AB testing real world with a dozen variables after someone buys two cars or is willing to swap wheels/tires over for testing purposes. The guys over at ecomodder.com do that kind of insane effort testing but I'm too lazy and I don't have a Model 3.

 

[FlyingKiwi]

The test was on a dyno, think of it as a stationary treadmill for cars. There is no aero in the test results because they are synthetic.

For gas cars they put a big fan in front of the car to keep the engine from overheating. For an EV they wouldn't bother.

That chart did not come from dyno testing, it came from ABC coefficients that are derived from (as far as i am aware) coast down testing.. so the data in the chart is entirely aero, rolling drag and transmission losses. so yes, the aero is represented in that chart.

 

[SageBrush]

I've been told by someone I trust that the ABC coefficients do not map neatly out to specific car forces; they do provide an accurate curve for forces acting on the car.

 

[SageBrush]

That chart did not come from dyno testing, it came from ABC coefficients that are derived from (as far as i am aware) coast down testing.. so the data in the chart is entirely aero, rolling drag and transmission losses. so yes, the aero is represented in that chart.

I keep thinking that drivetrain losses would occur in both the roll down and the dyno test. If that is correct then the EPA has to avoid double counting by excluding them somewhere.

 

[omgwtfbyobbq]

For what ?

I'm interested in range at 65, 70 and 75 mph cruising. I think that 70% of the raw highway result is a pretty good surrogate for 65 mph cruising, so that works out to 454*0.7 = 317 miles and therefore 78000/317 = 246 Wh/mile. The additional Wh/mile from higher speeds is easy enough to calculate ... or to just look up in my SS:

Newtons of Aero at
266, 65 mph -> 74 Wh/km
308, 70 mph -> 85.5 Wh/km
353, 75 mph -> 98 Wh/km

So taking the difference ...
70 mph is 11 Wh/km more
75 mph is 24 Wh/km more

Using 1.61 Km to a mile,
70 mph has 18 Wh/mile more consumption than 65 mph
75 mph has 38.64 Wh/mile consumption than 65 mph

Added all together,
70 mph is 246+18 = 264 Wh/mile and range is 78000/264 = 295 miles
75 mph is 246+38.64 = 284.64 wh/mile and range is 78000/284.64 = 274 miles

For being the only measurement of energy use at steady speed. The Crr is already there, which makes an accurate estimate of CdA fairly straightforward.

Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

With that, and an adjustment for what I'm guessing is ~200W of power required to keep everything powered, estimating range at different speeds is also relatively straightforward.

 

[omgwtfbyobbq]

I keep thinking that drivetrain losses would occur in both the roll down and the dyno test. If that is correct then the EPA has to avoid double counting by excluding them somewhere.

The coast down test is in neutral, and the results provide the road load parameters.

 

[FlyingKiwi]

I keep thinking that drivetrain losses would occur in both the roll down and the dyno test. If that is correct then the EPA has to avoid double counting by excluding them somewhere.

I guess they could do the coast down testing by removing the shafts from the test car and using a car with a big rubber bumper to push it up to speed? Unloaded transmission losses should be pretty insignificant, just a few pairs of bearings and fluid losses (hopefully warm fluid).

In the same context there are aero losses and tyre rolling losses from the rotating wheels on the dyno rollers too. They could use a hub dyno instead of rollers to reduce that

 

[FlyingKiwi]

The coast down test is in neutral, and the results provide the road laod parameters.

Do EV transmissions actually have a real neutral where the AC motor output shaft is not actually connected to the wheels mechanically? or do they just isolate the motor electrical circuits so there are no electrical effects and the rotor spins freely in its bearings?

 

[SageBrush]

The coast down test is in neutral, and the results provide the road load parameters.

What is neutral in an EV ?
If the car could coast when off, this would all make sense to me.

 

[omgwtfbyobbq]

Do EV transmissions actually have a real neutral where the AC motor output shaft is not actually connected to the wheels mechanically? or do they just isolate the motor electrical circuits so there are no electrical effects and the rotor spins freely in its bearings?

That's a good question. I'm guessing they just insure there's no regen when they cut power. Here's a relatively detailed description of coastdown testing from 1980.

Document Display | NEPIS | US EPA

What is neutral in an EV ?
If the car could coast when off, this would all make sense to me.

It's no regen and no power as far as I know. DW's Pip allows for coasting in N, and I imagine Tesla could modify the 3 to behave similarly even if the production version doesn't allow coasting so to speak.

 

[FlyingKiwi]

Here's a relatively detailed description of coastdown testing from 1980.

Document Display | NEPIS | US EPA

Thanks, i'll add that to the insomnia file

 

[Saghost]

Do EV transmissions actually have a real neutral where the AC motor output shaft is not actually connected to the wheels mechanically? or do they just isolate the motor electrical circuits so there are no electrical effects and the rotor spins freely in its bearings?

There are some PHEVs that do, and the Rimac rear transmissions can, but no, the vast majority of EVs can't physically isolate the drive motor from the wheels. It shouldn't be a big factor in the test, though.