# Drag Coefficient



## yamato (Feb 11, 2003)

Is there any one who can explain why the Drag Coefficient for a 3 series coupe is 0.1 higher than a 3 series sedan? :dunno: 

The spec says the coupe has a lower body and the wind shield is also placed "flatter". I can't understand why a coupe can have a higher drag... It does not sound reasonable to pay more to get a higher drag coefficient. 

Thanks.


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## nate (Dec 24, 2001)

It is wider


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## Kaz (Dec 21, 2001)

I'm not an aerodynamicist but I think nate is right. The rear of the sedan narrows quite a bit, but remains on the tall side, both of which I believe aid in aerodynamics.


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## Mr Paddle.Shift (Dec 19, 2001)

What really intrigues me is how MB E class attains a 0.26 Cd. Simply amazing.


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## yamato (Feb 11, 2003)

thanks. I agree the extra width probably increases the drag more than the lowering of the body.

If I remember right, most Lexus are also in the 0.2* range. I guess there is a lot of room for improvement in a 3er.


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## Nick325xiT 5spd (Dec 24, 2001)

yamato said:


> *The spec says the coupe has a lower body and the wind shield is also placed "flatter". I can't understand why a coupe can have a higher drag... It does not sound reasonable to pay more to get a higher drag coefficient. *


You pay more for a less rigid chassis, as well. What's your point?


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## The HACK (Dec 19, 2001)

VinceTopasBlau3 said:


> *What really intrigues me is how MB E class attains a 0.26 Cd. Simply amazing. *


It's not hard to create a car with low coefficient of drag. It is HARD to engineer a car without significant LIFT.

Take that same E class up to 150 mph and see if it's more stable than the 330i/Ci. Remember how the McLaren/Mercedes LeMans disaster?


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## yamato (Feb 11, 2003)

*Re: Re: Drag Coefficient*



Nick325xiT 5spd said:


> *You pay more for a less rigid chassis, as well. What's your point?  *


I guess reasons for most people who purchase coupes over sedans would somehow hope for a better look and a little better performance? For me sacrificing some comfort, safety, $ ... does not matter too much. Drag coefficient is part of a performance parametrics which is nice if it is lower than a sedan.

Anyways, feels better now knowing the LIFT is another factor to consider. Thanks guys!!


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## XKxRome0ox (Mar 3, 2003)

the "problem" is that BMW just took the basic sedan design... and adjusted a little to make the windshield more angled and did stuff to make up for the lack of an additional pillar that the sedan has in between the front and rear doors... 

i personally prefer the look of the coupes over the sedan... 
but in terms of engineering, BMW did a better job with the sedans because the sedan is the original design and the coupe is a tweaked version of it


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## Rotorblade (Nov 5, 2017)

If the coupe has a lower body, it may have slightly higher Cd but the airdrag takes into account frontal area too which gives you CdA, and if you say the coupe is smaller in height, it should have lower frontal area reaulting in less airdrag. For example Bmw i8 doesn't have a very low cd(.26) but it has very small frontal area.


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## STR8-6IX (Dec 6, 2017)

Rotorblade said:


> If the coupe has a lower body, it may have slightly higher Cd but the airdrag takes into account frontal area too which gives you CdA, and if you say the coupe is smaller in height, it should have lower frontal area reaulting in less airdrag. For example Bmw i8 doesn't have a very low cd(.26) but it has very small frontal area.


Theres much more to it then just the shape of the front.... And 0.26cd is a rather low number...


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