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Extrapolation of Range and Battery Size(s)

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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.

Yes, and it is EPA range we are talking about, not Wh/Mile at set speeds. It's a lot of stop and go and the weight penalty brutalizes range.

The i3 is currently the most efficient car on the road, tested by the EPA

i3
~2600lbs/22KWh/81 mile EPA range. = 3.68 mile/KWh, for 215 miles = 58.4 KWh.

It would be freaking amazing if the Tesla M3 which will probably weigh 1000+ lbs more, could actually come near the i3 efficiency.

It's total fantasy to think it would be significantly better than the flyweight i3.

The M3 pack will be at least 60 KWh.
 
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.
I think it's possible. The S85 is already more efficient than the i3 at a steady cruise.

http://avt.inl.gov/pdf/fsev/fact5658bmwi32014.pdf

http://avt.inl.gov/pdf/fsev/fact4500tesla2014.pdf

The weight difference between the S and the i3 is why the i3 gets better mpge ratings. If Tesla can shrink that difference to ~800lbs while substantially reducing CdA, the 3 will likely have a higher EPA rating than the i3.
 
If the S60 has an EPA rating of 208 miles, then a 4% efficiency improvement cumulatively due to the motor/inverter/battery pack improvements will give the 3 a range of 215 with a 60 kWh pack.

This is not counting lets say a weight loss of 10% (due to higher density, smaller physical pack, smaller dimensions), less frontal area, slight bit less rolling resistance, or 10% improvement in cD, and little things like less power draw for electronics(ie; single 15 inch monitor, fewer LED's, smaller standard speakers), more efficient cooling/heating ventilation system(mentioned in test ride), etc.

Considering all those factors, a 55 kWh battery pack may be able to do 215 miles, and works out to be just about 20% less than a 70 kWh currently offered (70 kWh minus 20% is around 56 kWh).

Also using the weight density of the old 85 kWh pack, a 55 kWh pack will weigh in at most 776 lbs and a 60 kWh pack will be at most 847 lbs. Going from a 55 to a 60 kWh pack gains at most 70 lbs. So, question we have to ask is have they made enough efficiency improvements altogether to shed another 50-60 lbs (remember this is Tesla, they don't include a spare; reason being the weight will hurt range) and just go with the 55? This will also give them some bragging rights saying they can do more with less compared to a Bolt.

I'd like to go with a rough number like 58 but Tesla plays with increments of fives. So, I'll just go out on a limb here and say they'll go with a 55 rather than a 60 (More with less as their motto) if they have made enough efficiency improvements throughout.
 
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IMO, the 3 will be more efficient than the i3 during stops (less power draw), steady cruise at 55, 65, or 75 mph (due to lower cD), and possibly during regen braking (more mass, more aggressive regen?) only losing out to i3 during acceleration runs on the EPA cycle (due to weight). Little things like how often and hard they accelerate during those acc. runs will give us a good hint as to what to expect. But if even half the EPA cycle is steady state cruise with plenty of stops, the 3 may be able to do it with a 55 kWh pack.
 
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.

While you can't buy a new Model S 60, keep in mind that it's EPA rating was 208 miles. 215 is 3.3% higher -- and low rolling resistance tires get close to providing a 3% efficiency gain.

The Model 3 will be more efficient than a Model S... Battery will be either a 50 or 55 depending on how comfortable Tesla is in beating the 215 minimum target.
 
And low rolling resistance tires get close to providing a 3% efficiency gain.

Is this true? Not saying I don't believe you but has this been proven/verified with some aftermarket low resistance tires? If so, I think it's a given the 3 will have at most a 55 kWh.

All things being equal (even weight), if the S60 had a 55 kWh pack instead, it would have had 190 miles of EPA range, so consider that they have to make up just enough ground for 25 more miles. Sounds pretty easy given 10% reduction in just weight and cD*A.
 
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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.
 
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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.

A lot of the things you mentioned DO NOT scale with weight or volume though. And a 20% reduction in volume doesn't correspond with a 20% reduction in weight, power draw, etc. either (If only life were this easy, haha) I'll be amazed if they can pull it off with a 50. Highly improbable.
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
 
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Let's also be optimistic and say Tesla can get the cost per kWh down to $100 by 2020. That means they save at least $500 per car if they drop down 5 kWh per any given model 3 they manufacture. If they make 500,000 model 3's by end of 2020 (not all in one year), that's a net savings of at the very least $250 million! And that's just on the model 3's alone.

This is as much savings as they got in deposits these past few days, so imagine all the deposits disappearing. That's the cost of going to a 60 kWh. I'm sure they have thought about the savings and are trying any which way to make the car just a wee bit more efficient to eke it out with a 55 pack at least for the first couple years.
 
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I find this photo a nice place to start guessing games:

ev-CdAs.jpg

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.
 
A lot of the things you mentioned DO NOT scale with weight or volume though.

It'd help me understand your point if you could be specific and argue how each individual component would scale instead. I agree there is a case to be made that some parameters will rather scale with the cube-square root instead. That's 85% instead of 80%. Total power draw would then become 3332W + 2820W + 4100W. That puts us at 64kWh before brick protection. But I took a very large brick protection : 9kWh (more than the current 85 model S) partially to offset this low ball number. 6kWh is an equally likely reserve so I think my numbers in the end up hold up pretty well.

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

I am looking forward to your model.
 
i3 advertises 206.4Wh/mile (12.9kWh/100km) .
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 ;-)
 
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

Yes. My thoughts exactly.

They are not fighting to shave 5KWh off the pack.

They put in a 60 KWh pack and keep refining the car towards production. Today they know they can achieve ~215 miles with the prototypes, and think they can do better with the final production model.

I think this is more about where final range lands with a 60KWh pack, than about how much they might shave off the pack.
 
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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 ;-)

I actually threw some numbers into a model, and only at about 30 mph or below is an i3 likely to be more efficient than a M3. Even at 40 mph, an M3 uses less power than a non-REx i3. Aerodynamics kick in quickly. The assumptions are about .47 meter-squared CdA for the M3, 0.7 meter-squared for the i3, 1250kg and 1750kg for respective weights, and 0.007 rolling resistance for both. The i3 already has pretty special tires, and what Tesla has asked Michelin for -- based on Michelin's public comments -- are likely to be at least as good. Low rolling resistance minimizes the effect of weight differences. I would bet a very large sum of money the base battery in the M3 is 55 kWh or less. And I suspect I'm a little conservative on the M3 CdA, as I'm using an A that's conservative.
 
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