Aerodynamic versus aesthetics, range, price, sales

Aerodynamic versus aesthetics, range, price, sales


I wonder why Tesla did such a current trend looking car when they have the opportunity to break ground in the aerodynamic.The people are so enthusiastics and Elon promised a revolution after having said that everything else was given (electronics, batteries, safety)

The only thing missing is aerodynamic that would improve range by roughly 15% for the same battery capacity. That is a lot for the sake of style. Everything else would be the same. This could translate by more profits for Tesla, more range for us, less lithium mines, lighter car, cheaper car, etc.

I am almost sure that with proper care for look, after aerodynamic, the M3 would have been acclaimed as well. Most early adopters are technically versed and aerodynamics would have been a plus.

At first I though that look and accelerations was utterly important for sales but:
Prius sell by millions copies does not look particulary good has small wheel, accelerate just ok etc, it's good thing are good inside space and to help the environnement.
Leaf sell well too and is years behind.

So why hold back with a look that will not stand out for many years ? (look awesome still) I have a gen 1 insight and I find it look really good, because it's efficient. This car make sense even if there is a lot of compromises. I dont beleive that every car will look the same being aerodynamic, birds come in differents look and most are efficient, same for fish like tuna and shark, both are really slippery and fast but look entirely different.

Just my opinion here, I just want to hear/read what others think about this.

DTsea | April 12, 2016

Tesla already is the lowest drag production car. Far better than prius. That is WHY it is a beautiful shape.

Tropopause | April 12, 2016

.21 drag coefficient IS ground breaking considering you can get five people inside COMFORTABLY.

Tropopause | April 12, 2016

Prius is only .25 drag coefficient AND it is ugly. Tesla knocked this one out of the park with best drag coefficient AND great looking.

What's the problem here?

jordanrichard | April 12, 2016

Also, Tesla is trying for a mass appeal and drag coefficient numbers mean nothing to the general public. Go ahead and tell any John/Jane Q public the drag coefficient of a car and you will get a blank look as in, "what does that mean to me?" Tesla is not going after early adopters with the M≡. They are going for mass appeal.

yongliangzhu68 | April 12, 2016

@ michelcotee: Name 3 cars that have ever been produced with a lower drag coefficient.

Sparky | April 12, 2016

That's why they'll put any nose tweaking into the wind tunnel to end up with the lowest C/D possible, which will probably be the most beautiful as well, though not necessarily due to the compressibility of air and Bernouli's theorem. If they could drop the mirrors it would be even better but they can't. Dumping the front plate in places where it's currently required would help though.

DTsea | April 12, 2016

Sparky, compreasibility effects dont enter at automotkve speed (mach .1). No shock waves on a road car.
Its all about turbulence (eg aft body shape) and excrescence (eg mirrors).

Sparky | April 12, 2016

It's not the shock wave but the compressed bow effect which can make an airflow effect from a flat surface. i.e.: if you look at the 3 front end the airflow is designed to split around the shape below the lip and smoothly over the top. Faster airflow has less pressure and stopped airflow makes a shape that you can't see.

michelcotee | April 12, 2016

I understand mass appeal, but just say that you could have 250 miles range instead of 215 miles because of Cd That just tell what it is.

Cd of 0.21 is 'hopefully' commented by Elon himself. Not official and measured fact as I understand.
This car will end up at best at Cd of 0.24. This is my personal opinion based on the look of others similar car.
Maybe Tesla as worked some magic like active bondary layer control
Just have a look at Volkswagen XL1 that is Cd 0.196 This is a production car, the only one I know. Others are prototype like Aptera of ford probe IV to name a few cd around Cd 0.16 so there is place for a lot of improvements, why make a incremental one ?

If it's 0.21 that will be awsome.
The EPA rating will tell how efficient overall. Unfortunately that number will encompass every systems.
If it happen this rating will be EPA <= 16kWh/100km or 258Wh/mile.

jordanrichard | April 12, 2016

The XL1 is a production car? Since when? Just how many people can fit in the XL-1? From my understanding, even for the 2 people in the car, the seat arrangement is skewed. Oh and that will not appeal to the masses.

You want ultimate aerodynamics, have a car where everyone lays down.

damonmath | April 12, 2016

@jordanrichard +1 - I was thinking the same thing. A bobsled.

Red Sage ca us | April 12, 2016

jordanrichard: Better yet...? A car where no one actually rides in it, they just recline in chairs and wear Virtual Reality headsets.

Bighorn | April 12, 2016

You can get another 35 miles of range tweaking Cd a few hundredths? Please show your math.

DTsea | April 12, 2016

Sparky, 'compressibility' to an aerodynamicist refers to entropy increases due to shock formation. Of course all bodies moving through a fluid have a stagnation point at which local pressure equals dynamic pressure (static pressure + .5×densityxvelocity squared) but us aero types dont refer to that as compressibility effects because ideal gas theory predicts that flow pretty well (no energy loss in expansion or compression) with a viscous boundary layer correction. In high speed flow, energy dissipated in shocks has to be considered- THAT is a compressibility effect.

Sparky | April 12, 2016

DTsea, Perhaps my terminology doesn't match the lexicon of aerodynamicists but would you agree that the design of the car in terms of aero is intended to be most efficient in the low speed flow regime? (under 100mph) And that the bending of the airflow includes local stagnation and higher speed flow creating lower pressure in areas where that is desired?

By the way, you're a good person to ask; how much would a licence plate stuck right in the front affect the overall aero efficiency of the car? Enough to make it worthwhile to get rid of it for that reason?

alnrench2 | April 12, 2016

EVs in states that require a front "plate" should be allowed to have an optional vinyl adhesive sticker "plate" on the front to keep drag at a minimum.....smooth, unobtrusive, easy to install and simple enough to remove or cover with a new one....and cheaper to produce !

ejlada | April 12, 2016

So at that point we're basically painting registry numbers on the hull? Dibs on NX-74205.

topher | April 18, 2016

"So at that point we're basically painting registry numbers on the hull?"

I wonder if anyone would notice...

Chunky Jr. | April 18, 2016

If it were more aerodynamic but ugly it would have flopped big time.

mos6507 | April 18, 2016

"This car will end up at best at Cd of 0.24. This is my personal opinion based on the look of others similar car."

Teslas have very smooth belly-pans which do a lot to lower drag vs. similar-looking ICE vehicles. So you can't make such a superficial guestimate.

Red Sage ca us | April 18, 2016

Hmmm... NCC-EL-29063, maybe...?

topher | April 25, 2016

"You can get another 35 miles of range tweaking Cd a few hundredths? Please show your math."

Simple version: going from 0.24 to 0.21 is a 12.5% improvement. Power for driving at speed is proportional to Cd, so for long distances, will give a 12.5% improvement in range times 215 miles range is 27 miles.

Long version: Power for long drives (thus ignoring braking or rolling losses) = (1/2 * ρ * Cd * Af * v³) / eff
Assume 70 mph, and 80% efficiency
if we use drag area from the Model S, we get: (1/2 * 1.3 * 0.24 * 2.3 * (3.1)³) / 0.80 = 13.3 kW
For 70 kWh of usable battery that gives 366 miles of range (theoretical maximum with large grains of salt)
replacing 0.24 with 0.21, we get: (1/2 * 1.3 * 0.21 * 2.3 * (3.1)³) / 0.80 = 11.7 kW
For 70 kWh of usable battery that gives 419 miles of range (theoretical maximum with large grains of salt)

So, for a 70kWh Model S, driving non-stop at 70 mph, absolutely best case scenario, going from Cd of 0.24 to 0.21 gives 53 more miles of range.

Thank you kindly.

topher | April 25, 2016

85kWh Model S (70 kWh usable).

MarlonBrown | April 25, 2016

It has been proved over and over again that ugly, exotic and weird looking cars have no success. Tesla has done a great job. | April 25, 2016

@topher: Here's an approach to looking at the effect of drag on a Model≡. For example the MS85 consumes about 140 wh/mile due to rolling friction and about 180 wh/mile due to air friction at 65 mph.

If the M≡ is 20 % lighter, has 20% smaller cross section an 10% smaller coefficient of drag for example then one would expect the energy consumption at 65 to be about .8X140+.8X.9X180=112+130 = 242 wh/mile. The EPA rated consumption for the MS85 is about 279 wh/mile, 87% of the 65 mph consumption used above. This suggests that the EPA number for the M≡ will be about 211 wh/mile. 215 estimate miles of range therefore suggests a battery pack with a useable capacity of 45 kWh, with some reserve, the rating of the pack then would be over 50 kWh.

Personally, my gut feel is that 10% less drag than .24=.216 is too aggressive and it will wind up being more like .23. And the battery will be more like 55 kWh.

BTW: 12.5% smaller drag coefficient by my estimation produces a range of 274 at 65 for a Model S70D, 19 miles more than Tesla's 255 mile number on the website. You used 70 mph in your example. 70 vs. 65 is only about 16% more drag. That would increase the differential to only about 22 miles as opposed to your 53.

Bighorn | April 25, 2016

Thanks George for pointing out that there are signifIcant factors ie rolling resistance, amongst others, that can't just be yada yadad out of the calculus. Unfortunately, JB's white paper about Roadster efficiency seems to have the data redacted.

adoh2010 | April 25, 2016

Check this out:
Five slippery cars enter a wind tunnel; one slinks out a winner. - Tesla Motors

The Model S has a lower effective frontal area than every other compact and midsize sleek sedan, the power used for drag resistance at 70mph is only 14hp, or 10.44 kW. Assuming that the tesla 90D gets 300 miles of range, this means that 44.74 kWh were used to resist air. Assuming discharge and parasitic losses and drive train efficiency means that 70 kWh of energy makes it to the wheels out of the 90, this still leaves over 25kWh being wasted on tire rolling resistance and bearings friction. You guys are treating non-drag losses like they're negligible. A 10% lower effective frontal area would translate to 6-7% highway range increase, and will compromise interior space because this is already a well designed car.

If any Model S owner is as curious as I am to know the exact non-drag losses please drive at 70mph on a smooth, flat road and tell us the kW consumption number shown by the computer. Minus 10.44 and there you go.

adoh2010 | April 25, 2016

"Assuming that the tesla 90D gets 300 miles of range"

At 70mph I forgot to mention.

Ross1 | April 25, 2016

Over 100 mph is irrelevant.
Over 70 mph is irrelevant.

Badbot | April 25, 2016

I vote for 4" wide 12 ply tires with 80 psi in them to lower rolling resistance!
OK so it rides like a Conestoga wagon but the range should go up. and who needs to turn or even stop?