You can install our site as a web app on your iOS device by utilizing the Add to Home Screen feature in Safari. Please see this thread for more details on this.
Note: This feature may not be available in some browsers.
So, 18.8kWh at 129Wh/km gives about 146km, or about 91 miles, not 81. But, I suppose that's "this is what it can do" vs. EPA.
I think it's possible. The S85 is already more efficient than the i3 at a steady cruise.i3 is still about 10% better than a Model S on the EPA highway as well. EPA "highway" test has lots of stop and go. It is unrealistic to expect the Model 3 to come with less than 60 KWh battery and get an EPA range of 215 miles.
Even the most efficent EV you can buy today would require almost 60KWh to have 215 miles of EPA range. And that would only be true if it gained no weight while upsizing the pack from 22 KWh to 60 KWh and we know that isn't true.
EPA test is heavily influenced by weight, both on highway and city numbers, so anyone fiddling around with numbers showing packs significantly smaller than 60KWh is just blowing against the wind.
And low rolling resistance tires get close to providing a 3% efficiency gain.
Let's do physics : there are three components of work an electric car in motion needs to deliver. The rolling resistance from the tires, the drag resistance from moving through air and finally the static load like keeping the battery and car itself at temperature.
For a model S 85 I take weight 2000kg and tire rolling resistance coefficient 0.009, frontal area 2.35m^2 and Cd of 0.24. At 80km/u we get for the rolling resistance 80/3.6*m/s*2000kg*9.8*m/s^2*0.009 = 3920W. For air drag we get 0.5*1.225km/m^3*(80/3.6m/s)^3*2.35m^2*0.24 = 3790W. Assuming a model S using 78kWh travels 500km at that speed=6.25 hours. So it really draws 12480W from the battery. Substracting air and tire resistance that gives us 4770W for the static load.
How do all these numbers change for a model 3 that's 20% smaller in volume?
Rolling resistance scales with weight which we assuming more or less equals volume : 3136W. Air resistance Cd becomes 0.21 and frontal area becomes 85% (=0.8^3/2) of 2.35m^2 = 2820W. Let's assume 300W of the static load is indifferent of the car volume (on board computer system, screen, lights, ...) and the rest scales with volume (AC, keeping battery on temperature, inefficiencies in inverter, ...) = 3876W. Total power draw of the model 3 according to this model = 9832W. To reach equivalent S85 range (500km at 80km/h steady state) we'd need 61.5kWh plus bricking reserve. Let's be generous and say 70kWh. The model 3's base range is more like a S60 range. Proportionally this comes down to just under a 50kWh battery.
I find this photo a nice place to start guessing games:
A lot of the things you mentioned DO NOT scale with weight or volume though.
Also I think it's best to use the EPA test as the standard which as mentioned has a lot of stop and go, not just steady state cruise
Nice catch! Either their arithmetic is off or Cd and/or frontal area is wrong.Yet it seems they flubbed the Model S drag area?
If the Cd and frontal area numbers are correct, the drag area should be 6.0 ft^2.
At fueleconomy.gov the window sticker is reported as 250 Wh/mile city, 300 Wh/mile highway.i3 advertises 206.4Wh/mile (12.9kWh/100km) .
Elon's reply was "hopefully 0.21", which to me means that is what they are trying to end up with. So the current range of 215 miles is not with a cd of 0.21 but the base range will improve if they can reach 0.21
At fueleconomy.gov the window sticker is reported as 250 Wh/mile city, 300 Wh/mile highway.
At ~ 65 mph, aero resistance is about half of the total. Since the M3 might weight some 50% more than the i3 but the i3 has a 50% greater CdA, that would suggest that the T3 will end up having a similar highway energy consumption of 300 Wh/mile. Note however that this includes charging losses, so the on-road consumption is around 85% of that amount, or 268 Wh/mile. If we say that 15% of the nominal battery capacity will be a reserve against bricking, we are back to 300 Wh/mile.
This is considerably more than the drag equation suggests, so there you are. Pick you favorite number and make yourself comfortable for the wait ;-)