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## What does Tesla mean by a 200 mile range Gen 3 car?

## What does Tesla mean by a 200 mile range Gen 3 car?

Submitted by Gen3Joe on Fri, 2014-07-04 08:34

TM keeps saying they will offer a 200 mile car in the Gen III. When they discussed plans for the Model S they always talked about it being a 300 mile car. 300 miles ended up being the maximum ideal range of the most expensive model that they were referencing. Either they have learned from that and are doing a better job of managing expectations this time (I.e. quoting the real world range of the base model instead of the ideal range of the extended range model) or the Gen 3 is going to have a maximum range of 200 miles for any model option. I know this has been discussed here and there on many other threads but I thought it would be good to get everyone's thoughts on this in one place.

What do you all think?

Iowa92x| 4 juli 2014The base Gen 3 will have a 60 kWh pack, good for well over 200 miles. I think the starting price will be closer to $40,000 than $35k.

Gen3Joe| 4 juli 2014I'm thinking they'll put however many kWh needed in the base model pack to get just over 200 mile EPA rated range. I don't think Elon Musk wants to offer a Tesla vehicle with under 200 mile range ever again. I'm hoping they will offer another 75 miles of range or so for around $7500 extra. Performance model with the extra range for an even $50k before options would be awesome!

I think most likely you are right though the base model will end up being closer to $40k.

Brian H| 4 juli 2014Elon's wording was "a minimum of 200 miles".

Red Sage ca us| 5 juli 2014A Matter of Principle, Procedure, and Percentages...

Gen3Joe wrote, "I'm thinking they'll put however many kWh needed in the base model pack to get just over 200 mile EPA rated range."

The EPA changed the way that they tested cars, just in time to test the Tesla Model S variants. Tesla Motors was certain that the EPA ratings would be something like:

kWh Range

40 180

60 240

85 300

They were surprised that the addition of new cycles of testing, and changes to the specifics of the older ones, meant that the cars rated lower across the board on overall range. It also didn't help that the EPA seemed to purposely mark down mileage they had actually achieved, to account for a 'margin of error'. The result is that the final EPA ratings for both overall range and the newly devised MPGe ended up being only around 90% of what Tesla had expected to receive.

Tesla will not make that mistake again. They have promised a 200 mile range minimum. They will be raked over the hot coals of criticism by the entire automotive industry and the automotive and financial press if the next car gets an EPA rating of 'only' 197 miles.

Some had intimated that with a 20% smaller car, Tesla could manage to get 'up to' 200 miles range with only a 48 kWh battery. Maybe so. But if the car achieved 205 miles, and the EPA chose to knock off 10% again, that would drop them down to only 185 miles. Absolutely unacceptable.

That is why Tesla must go with a battery capacity of at least 60 kWh. In a vehicle weighing as much as 3,700 pounds, they should be able to achieve an EPA range rating of about 250 miles, out of an estimated 278 'ideal miles'. It also allows a bit of a buffer, just in case the EPA introduces more changes to their testing procedures, just before the release of GIII that might effect its perceived total range.

Gen3Joe| 5 juli 2014@Red Sage

I have never agreed with people stating that the Gen 3 car could get over 200 miles range with just 48kWh in the battery. The Leaf averages around 230 Wh/mi and has a 23k pack and an EPA rated range of 76 miles. If it were doubled to 46kWh the a Leaf would still only manage a range of 154 miles. If Tesla had a smaller cross sectional area and as good or better drag coefficient it might be able to manage 170 miles of range. It would be well short of the 200 mile mark though for sure and I agree with you that anything less than 200 miles of range will be unacceptable.

Gen3Joe| 5 juli 2014I should also mention that the weight makes almost no difference to range in highway/freeway driving all other things being equal. The only time weight comes into play at constant higher speed is during elevation change. So the Gen 3's weight advantage will only help range in city driving where the inertia of the car has to be overcome repeatedly during stop and go.

Red Sage ca us| 5 juli 2014Gen3Joe wrote, "The only time weight comes into play at constant higher speed is during elevation change."

Please explain this curious phenomenon.

Gen3Joe| 5 juli 2014When a car is traveling at a constant rate of speed, especially at freeway speeds, it makes very little difference how much it weighs. The overwhelming majority of the power (and energy over time) is used to overcome the resistance of the air. The power required goes up exponentially with the velocity travelled.

The drag coefficient, the cross sectional frontal area of the car and the velocity all factor into the equation. The extra friction due to the weight of the car is minuscule in comparison.

Gen3Joe| 5 juli 2014On the other hand, the mass of the car makes a significant difference when that mass has to be lifted a few thousand feet against the force of gravity to ascend a mountain. The more mass the more energy required to ascend the mountain.

Red Sage ca us| 5 juli 2014Gen3Joe wrote, "The drag coefficient, the cross sectional frontal area of the car and the velocity all factor into the equation. The extra friction due to the weight of the car is minuscule in comparison."

So... Weight has nothing to do with responsiveness, handling, acceleration, or range...?

Please explain the reason for a Gross Vehicle Weight Rating, or for Tow Ratings, if the weight of the vehicle, or its contents, or what it tows are of no meaningful consequence on range or energy required, once the vehicle is moving at speed.

Gen3Joe| 6 juli 2014Red Sage - I just did explain. I never said anything about responsiveness, handling, acceleration, and I didn't make a blanket statement on range.

Once a vehicle is at speed (e.g. 65mph) and maintains a constant speed weight is no longer a factor of any significance.

Iowa92x| 6 juli 2014Joe and Sage are both correct, just have a wire crossed. This sums up the weight/speed factor.

For city driving, weight of the vehicle has the largest impact on range. Lots of accelerating and braking means mass matters.

For highway driving, speed of the vehicle has the largest impact on range. Air resistance is what matters to range.

Factors like elevation change or pulling a trailor modify the scenario. Going up a mountain at 60 mph, you are dealing with air resistance and gravity, so both wind drag and mass eat the watts.

Timo| 6 juli 2014Rolling resistance is directly related to vehicle mass (and in RL speed). However it's linear relation not square like air resistance, and it doesn't start at zero, so at low speeds rolling resistance is major loss, and in higher speeds air resistance is dominant loss.

http://en.wikipedia.org/wiki/Rolling_resistance#Depends_on_applied_torque

In case of Model S the cross-point of those two is about 50mph. Up to that point rolling resistance is higher than air resistance. Mass matters.

centralvalley| 6 juli 2014Just remember ol' Isaac; a body in motion tends to stay in motion unless acted upon by an outside force. Conversely, a body at rest tends to stay at rest unless acted upon by an outside force.

Inertia!

(I am no physicist; however, is it not true that mass does not equal weight? I always thought that mass was constant; weight is dependent upon many factors.)

Timo| 6 juli 2014Mass does not equal weight. Correct. Weight is caused by acceleration. In normal meaning of the word, acceleration caused by Earths gravity (g).

In orbit where you are free-falling toward Earth but are going so fast sideways that you keep missing it, you are weightless, because there is no acceleration affecting your body.

Gen3Joe| 6 juli 2014The force required to overcome drag goes up by the square of the velocity. The power goes up by the cube of the velocity.

@Timo

I would be curious to know where you got your source for the 50mph intersection of force required to overcome rolling resistance and air resistance. I'm not doubting it I'm just curious. It would be interesting to see how much horsepower is required to maintain speed at 70mph cruising speed for a 4700 pound car vs the horsepower for a 3700 pound car to overcome rolling resistance. Same for air resistance. The car should have the same drag coefficient and cross sectional area to make it apples to apples.

Gen3Joe| 6 juli 2014I did some more reading on this since Timo's post got me curious. It does appear that 50mph is a good approximation for where both of these forces meet. The rolling resistance is constant (i.e. Not a function of velocity). Without doing the math I was guessing that rolling resistance would only matter around town at speed under 40mph or so. Looks like I was wrong.

It is true that air resistance is king at freeway speeds though. Rolling resistance is not minuscule as I stated before (thanks Timo).

I still think a 48 kWh battery is not going to take the Gen3 car anywhere near 200 miles when at freeway cruising speed. To make it 200 miles the driver would have to compensate by dropping their speed and we all know how Tesla feels about compromise! I would love to be proven wrong about this:)

Timo| 6 juli 2014There was a good deal of discussion about this couple of years ago, and also couple of very informative blog posts in blog section of this site (even including an excel sheet which you could enter your own numbers and check the resulting range/consumption/curves).

Gen3Joe| 6 juli 2014Thanks Timo!

I just created my own excel sheet to calculate the power needed to overcome both rolling resistance and air resistance. The point where the two lines cross is between 60mph and 65mph. Boy was I wrong! This will teach me to do the math before running my mouth based on assumptions. If I new how to post pictures from my local drive I would post it here.

After adding both factors (not including drivetrain friction loss) the power to maintain 68mph for the Model S and Gen 3 car assuming the Gen 3 is 3700 pounds, has the same cd and 20% smaller cross sectional area is the following:

Model S: 23.1 HP

Gen 3: 18.4 HP

So the Gen 3 needs roughly 20% less power to travel at cruising speed than the MS. It's funny how the math works out that when you make the car 20% smaller you need 20% less power roughly at freeway cruising speed.

The one assumption that is most likely wrong is the 20% smaller cross sectional area. That I feel will be hard to achieve without cramping the passengers.

Will 20% drop in power required result in 20% longer range? It seems intuitively like it would but I really have no idea.

Timo| 6 juli 2014That assumption about Gen 3 being 3700 pounds might be optimistic. If they use steel it is comparatively heavier car, and also about 3000 pounds from Model S weight comes from other things than frame and panels. Gen 3 might well be over 4000 lbs car even that it is roughly 20% lighter.

I hope they manage to shave off some weight from those other things.

Timo| 6 juli 201420% lighter = 20% smaller (obviously)

Timo| 6 juli 2014Clarification: typo. Need coffee...

Red Sage ca us| 6 juli 2014I got the estimate of 3,700 pounds from two things: 1) Elon Musk saying the GIII would compete with the BMW 3-Series; and 2) his also saying the GIII would be 20% smaller than Model S. They seem to converge. 3,700 pounds is right in the middle of the weight ranges of the lightest and heaviest versions of the BMW 3-Series. 3,700 pounds is pretty much exactly 80% of the published curb weight of the Model S. I doubt they can make the mark with steel as the primary material for chassis and body panels, it would likely end up being 4,000 pounds instead. I think they might be able to manage 3,400 pounds with aluminum construction on the entry-level rear wheel drive version of GIII. But as usual, these are merely guesses.

Brian H| 7 juli 2014There are steels, and there are steels. Zero-G alloys, f'rinstance ...