Car And Driver magazine's drag coefficient measurements

[MartinAustin]

The Slipperiest Car on the Road | Blog | Tesla Motors

I'm reminded of the scandal with the manufacturers providing fuel economy numbers to the EPA. They all make their own numbers up (or, use some sort of testing that is peculiar to each manufacturer and are not equally-weighted, like an independent measurement would be). Only when they are truly ridiculous do they get called out for making up fictitious numbers.

It's good to see coefficients of drag getting independently measured on the same equipment. Kudos to Car And Driver. Now we can really compare them. The Mercedes CLA250 measured number of 0.30 seriously calls into question Mercedes' own claim of 0.23, which is a significant difference. By comparison, right in line with our understanding of Elon Musk - who gives it to us straight, warts and all - the Tesla claim is 0.24, and Car And Driver measured 0.24.

 

[jerry33]

It's good to see coefficients of drag getting independently measured on the same equipment. Kudos to Car And Driver. Now we can really compare them. The Mercedes CLA250 measured number of 0.30 seriously calls into question Mercedes' own claim of 0.23, which is a significant difference.

My guess would be that MB is measuring just the body shape without the undercarriage and it's aerodynamically inefficient parts. It's easy to get very low numbers then.

 

[yobigd20]

odd that they measured the P85 to have 0-60 in 4.6 seconds and a quarter mile times of 13.3. that seems very slow compared to every other 0-60 and 1/4 mile measurement I've seen of a P85. then again, the one pic shows that they are using 19s. and its an early 2012 model. therefore, probably crap-ass goodyear tires that slip under full accel.

 

[3mp_kwh]

The 0-60 times can depend upon the "1 foot roll-out", and whether it is included/excluded at the start.

 

[stopcrazypp]

My guess would be that MB is measuring just the body shape without the undercarriage and it's aerodynamically inefficient parts. It's easy to get very low numbers then.

The article explained why. The US version of the CLA does not have the active grill shutters that the European version does. So it's still possible that the European version does have such a low drag coefficient.

 

[jkliu47]

A statement in the last paragraph is interesting -

"With taller gearing, a P85 Model S might reach 200 mph"

Could this be the German spec Model S of the future?

 

[sbronle1]

I saw that comment too and was wondering... "top speed is redline limited?" Is there really a limit? No one except a driver on a race track, someone drunk, or someone running from the law would ever drive that fast. It kind of reminds me of that old Nissan 200 commercial that ends by saying something like "you will never drive 150 mph but at least you know you could." Given the current size of the motor in a MS is only about the size of a gallon of milk minus the inverter, surely a larger one could ensue. Just thinking...

 

[AlexT]

A statement in the last paragraph is interesting -
"With taller gearing, a P85 Model S might reach 200 mph"
Could this be the German spec Model S of the future?

Aren't they often (software) limited to 156 mph (250 km/h)?
I would be curious to learn how it affects battery drain and temperature.

...Is there really a limit? ...

Centrifugal forces may pose some limits on engine parts.

 

[SebastianR]

Aren't they often (software) limited to 156 mph (250 km/h)?
I would be curious to learn how it affects battery drain and temperature.

Yes, they are. And then there is a whole host of companies that makes good money removing that limit...

I guess the bigger problem is that at 160mph the range of a P85 would look more like that of an i3 (at much lower speeds - granted)

 

[MartinAustin]

Perhaps this might better be placed in the "video" forum, but since it is related to this thread I thought I'd keep it here -

Aero Comparo! Tesla Model S vs Volt, Prius, Leaf, Mercedes CLA - YouTube

 

[Robert.Boston]

Yes, they are. And then there is a whole host of companies that makes good money removing that limit...

I guess the bigger problem is that at 160mph the range of a P85 would look more like that of an i3 (at much lower speeds - granted)

My understanding is that the limitation at 130mph is not just to limit energy consumption but also because of the RPM of the motor. To be able to sustain speeds above 130mph, Tesla will need to change the gearing ratio (or add a multi-speed transmission, unlikely).