Model Y vs. EV6 Cd Analysis

[Snax]

So I just bought a Kia EV6, and I am fascinated by the discrepancy in claimed drag coefficients of these two cars.

Their profiles are very similar, but Tesla claims 0.22Cd for the Model Y, while Kia claims what I feel is a more believable 0.28 for the EV6. So I am wondering if Tesla simply appears to be lying, or if there are some obvious improvements to aerodynamics that Kia left on the table that Tesla has not. I can't see much that would account for that much difference.

Thoughts?

https://photos.app.goo.gl/9WFpu8oatV7kWTEy7

[freebeard]

One should test both vehicles in both wind tunnels and average the result.

[Vman455]

The short answer is, cars aren't 2D bodies, don't have 2D flow fields, and so any analysis that relies on 2D assumptions (e.g. looking only at a profile) won't lead you to correct conclusions about their aerodynamic drag.

For example, this car has a drag coefficient of 0.24:



And this car with an identical profile has a drag coefficient of 0.21:

[Snax]

Great examples of what I am half-getting at though. Is it realistic to believe that whatever subtle changes Tesla did here really result in a drag coefficient difference so high?

I'll grant that the Model Y vs EV6 may not be a good comparison given the slopes of the back glasses. Kia obviously recognized there would be some flow separation off the roof or they would likely not have added the spoiler.

[aerohead]

The vantage point of the camera producing the images can distort the actual geometry of both cars.
A GOOGLE search produced blueprints for both cars, in at least three-views each, with dimensions.
The roofline of the KIA is 'discontinuous' with respect to the total length of the body and will offer a penalty in pressure recovery compared to the TESLA.
TESLA wheels probably also have an advantage.
The Hyundai IONIQ 6 sedan, with it's flow-mending rear spoiler represents a fine compromise roof contour.

[kach22i]

Every Tesla I've driven behind (except Cybertruck) has a distinct greenhouse taper to it (on the sides).

I doubt the Kia EV6 has the same 3 dimensional thinking behind it.

https://pluglesspower.com/learn/tesl...y-worth-money/


EDIT:

https://www.cochesyconcesionarios.co...v6-ev6_gt.html


Closer than I thought, but perhaps enough taper differences in plan to warrant the discrepancy.

That said, take any projection, promise or number provided by Tesla and just assume it's an overstatement.

At least that has been their track record.

[Hersbird]

The Ioniq 6 is the one to get if you want aerodynamics on the Hyundai/kia platform. You can see the difference in range the .21 vs .28 or .29 gets you.

[aerohead]

Rob Palin, aerodynamicist for all TESLA's uses Dassault-Exa PowerFlow CFD, which is known to generate Cd accuracies within 1% of those generated by full-scale wind tunnels.
The final 3-D data cloud, 'frozen' after testing, is what will generate the tooling used to manufacture the entire car.

[Logic]

Originally Posted by Snax

So I just bought a Kia EV6, and I am fascinated by the discrepancy in claimed drag coefficients of these two cars.

Their profiles are very similar, but Tesla claims 0.22Cd for the Model Y, while Kia claims what I feel is a more believable 0.28 for the EV6. So I am wondering if Tesla simply appears to be lying, or if there are some obvious improvements to aerodynamics that Kia left on the table that Tesla has not. I can't see much that would account for that much difference.

Thoughts?

https://photos.app.goo.gl/9WFpu8oatV7kWTEy7

Remember that 68% of fuel is used accelerating weight in city driving,
vs 14% for Aerodynamic Drag.
And that 98% of driving worldwide happens in cities.

"...For every 100-kg reduction, the combined city/highway fuel consumption could decrease by about 0.4 L/100 km for cars..." (not; just city...)
https://ecomodder.com/forum/showthre...ban-41665.html

So it's possible that some underfloor covers or something may be omitted in one make, as doing so actually drops the average...

ie: there is a fine line between weight adding aero and leaving it off as far as overall fuel consumption goes.
Such is the physics!

[Piotrsko]

Annnnddd being a test tech, where and how you put your sense devices, even the sense method, affects what data you get.