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Model 3 Battery size

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I'll leave it to you to calculate all the ratios, but here's how consumption changes by steady-state speed for a theoretical Model 3. Both graphs have the same data, just plotted differently (stacked vs overlaid).

At highway speeds between 65 and 75mph, overcoming aero drag consumes between 44 and 50% of the power per mile. Even out to 100mph, which I didn't include on the graph, the aero losses are only 61% of the total.

tbrw976.png
Is this because of the low (assumed) Cd? Everything I've read to date points to aero drag being the dominating force on most vehicles. I suppose the closer you get to a "frictionless" vehicle, the more the other factors matter.
 
@ohmman Basically yes, aero drag force is the dominate loss at faster speeds. In the upper graph you can see it becomes dominant at 54 mph. In my Bolt EV model, it becomes dominant at 37 mph.

But there are a number of factors at play since this percentage is a ratio comparing multiple loss sources. Increased weight and tire rolling resistance both change the total and hence the aero drag percentage of that total. Here are some more estimates for the aero drag as a percentage of power consumption at 75mph:

S 100D....50%
X 100D....48%
S 90D......51%
S 60........50%
3 xx.........50%
Bolt EV....66%

I would NOT pay close attention to the few percentage point differences in between the Teslas, but my calculations seem to show that the effects of a lighter weight and lower Cd Model 3 cancel each other out to match the Model S for this particular metric.
 
Thank you for your very helpful graphs and analysis. Very interested to note that Aero Drag Consumption does not increase as dramatically at freeway speeds as I expected it would. Can you explain why the absolute (not percentage) Ancillary Systems Consumption is slightly greater below 25 than over 30?
At highway speeds between 65 and 75mph, overcoming aero drag consumes between 44 and 50% of the power per mile. Even out to 100mph, which I didn't include on the graph, the aero losses are only 61% of the total.

tbrw976.png
 
I suspect the Model 3 has about 20% less space for the battery pack, right?
It is the battery area that counts (i.e. not the wheel/suspension and overhang) So are you sure about only 10% smaller?
The wheelbase of the 3 is only ~3% shorter than the wheelbase of the S:
fullvcqua9kx6h.gif

Going with the MotorTrend size estimates of the Model 3...
Model S: 77" wide, 116.5" wheelbase
Model 3: 74.2" wide, 113" wheelbase
Model S battery area: 8970.5
Model 3 battery area: 8384.6

The area between the wheels is 93% of what's available for the Model S. So we could end up seeing some rather large batteries in the 3.
 
Thank you for your very helpful graphs and analysis. Very interested to note that Aero Drag Consumption does not increase as dramatically at freeway speeds as I expected it would. Can you explain why the absolute (not percentage) Ancillary Systems Consumption is slightly greater below 25 than over 30?
The ancillary systems energy consumption is from a constant ~1kW power usage so it grows in significance as speed decreases.

There's always seems to be confusion between power and energy consumption. This is where many people get tripped up, myself included. Here are two more graphs of Power vs Speed [kW vs mph] next to the original Energy Consumption vs Speed [Wh/mi vs mph] graphs. (I previously mislabeled them power consumption, argh!) These graphs show results using the same model and input assumptions.

y2wRNuw.png


The graphs on the left show the energy consumption, which is energy needed to go a given distance, plotted against speed. The graphs on the right show the power needed to go a given speed, plotted against speed. The key is that as speed increases the time to go a given distance decreases.

On the left, you can see the aero drag energy consumption is increasing as a square of speed. The exponential growth in the equations is a V^3/V term that simplifies to V^2. On the right, you can see aero drag power increasing as a cube of speed. The equations have just the V^3 term.

(It might be interesting to note that the power vs speed graphs show four different power relationships. The ancillary systems power is constant over speed, a V^0 term. The tire rolling power is linear with speed, a V^1 term. Drivetrain power is a function of aero drag and rolling power and so is a V^2 term. [This is not strictly mathematically true, but close when aero drag and rolling drag are similar.] And of course aero drag power is a V^3 term.)

Ultimately, the power vs speed graphs on the right are not too relevant for discussions about EV range and efficiency. What matters more is how much energy is needed to go a given distance, as shown in the graphs on the left.
 
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...by creating larger packs for the MS and MX it allows Tesla to put a larger battery in the Model 3 while not appearing to be crossing into the MS territory. ... We know they will want some way to differentiate the M3 and MS and in many ways it appears that the size of the car is in large part going to be the only difference (at least from what we can tell at this point).
There is no need to 'protect' Model S sales. Tesla Motors will lose NOTHING when sales of Model ☰ begin. The Model ☰ will undoubtedly have higher range than Model S with a given battery pack capacity. The Model ☰ will certainly have a more aggressive Performance profile than the Model S. Just as the A4, 3-Series, and C-Class outsell their stable siblings in the A8, 7-Series, and S-Class while kicking their butts in fuel economy and Performance for less money. The Model ☰ will defeat its direct competitors in sales just as the Model S does the same to its own.
 
Garsh-
If you look at mdl 3 rear tire well-it looks too large toward the rear side of it. Hopefully tesla has fixed that.
The model S the space is equal all the way around the tire.
I had never noticed that before, but now that you've pointed it out, I can't un-see it.
Hopefully this can be chalked up to the fact that these cars are alpha prototypes, and body panel fitment will be better on production cars.

The black one seems to have the same issue:
ceef7ff5026ddd3efbdf279139382a9d.jpg
 
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Reactions: MissAutobahn
What is your evidence which is better than Teslas? How did you measure the Cd of the Model 3?

Thank you kindly.

I don't have any evidence, just existing cars Cd...

Motorburn | 12 of the most aerodynamic cars in production right now

In order to obtain a drag coefficient below 0,22 VW has to cover rear wheels.

According to the article the only commercial car whose Cd is below 0,24 (MS) is mercedes CLA (0,22).

It would be a surprise if they achieve a better Cd. .. but who knows? Tesla doesn't stop surprising the world.
 
According to the article the only commercial car whose Cd is below 0,24 (MS) is mercedes CLA (0,22)

The article is wrong. The Mercedes CLA was independently tested by Car and Driver Magazine at 0.30 drag coefficient. Currently, the Model S has the lowest drag coefficient of any production car. Elon said 0.21 for the Model 3 (Source). I would not bet against Elon.

 
Elon said 0.21 for the Model 3 (Source). I would not bet against Elon.
Elon said hopefully 0.21. That's different than saying it's going to be 0.21.

He has tweeted a number of things that haven't come to fruition. He's an optimist by nature. I'm not saying that they won't achieve 0.21, what I'm saying is that it's disingenuous or at least misleading to say that "Elon said 0.21." It'd be more clear to say "Elon is hoping for 0.21."

*edit -- and @Zoomit beat me by a minute.
 
Elon said hopefully 0.21. That's different than saying it's going to be 0.21.

He has tweeted a number of things that haven't come to fruition. He's an optimist by nature. I'm not saying that they won't achieve 0.21, what I'm saying is that it's disingenuous or at least misleading to say that "Elon said 0.21." It'd be more clear to say "Elon is hoping for 0.21."

*edit -- and @Zoomit beat me by a minute.

This identical argument is occurring on Reddit right now. Troy is stating assumptions as fact:

"Model 3" A Tesla employee/representative basically told me the Model 3 won't be a luxury vehicle. How is that true? • /r/teslamotors
 
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I don't have any evidence, just existing cars Cd...

Aerodynamic engineers have their own word for 1/10,000th of a Cd ('counts'). If I was one, and working at Tesla, I would be sure I didn't claim more than a few of those would be possible on a car already in prototype, and with a mere few months until pencils down. I certainly wouldn't let my boss say that we would squeeze 3 hundredths of a Cd in that time frame (300 counts). At most, therefore the Cd of the prototype would be somewhere in the 0.22 range.

Tatra 77A is an existing car (not in production since 1938) with (maybe) a Cd of 0.212

Thank you kindly.
 
Tatra 77A is an existing car (not in production since 1938) with (maybe) a Cd of 0.212
In the late '30th and in the '40th there was a few cars with some outstanding Cd clams, Tatra was one, and if I remember correct Tucker "Torpedo" '48 was an another, and I'm almost sure it was some others to. Has anyone tested them in a modern wind tunnel to verify this clams?