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      10-31-2012, 08:11 AM   #30
highrevs
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Drives: 2007 335xi
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Quote:
Originally Posted by THE-FN-MAN View Post
Impressive man! For shits and giggles where dues the M3 fit in with regards to aero compared to these two. My car is pretty much as modded as it can get short of a built motor and I hang with my buddies Z06 until about 4 when he starts to pull.
I had to take some liberties with the relevant specs for the M3 since we have coupes, sedans, and convertibles. Looks like 0.32 is the worst case drag coefficient from a post claiming numbers directly from BMW; usually take the worst case in these scenarios because you can say that in reality the results are probably better. For width and height I used the coupe values [1] (reason below).

Not surprisingly, it did pretty damn well. With respect to drag force it's literally right on top of the Z06; had to use some formatting trickery to distinguish the two. That's pretty impressive given that the Z06 is four feet tall.

The one big thing I would infer from this is that drag can probably be tossed out when comparing the M3 and Z06. So in theory if the two cars have the same power to weight ratios and other effects (like gearing and traction) are negligible the two should be very close. What kind of power are you putting down?

Take a look at the attached wind tunnel test of the M3 (why I went with coupe dimensions). It shows that any one method of testing or modeling isn't 100% accurate. What I'm guessing is the derived drag coefficient (0.33) isn't what BMW listed for the M3 coupe (0.30). Another thing it shows is that my model isn't 100% accurate because using width and height to estimate frontal area ignores the fact that the bottom of the car is several inches above the ground. They listed frontal area as 2.17 meters and based on width and height I calculated 2.57 meters. Of course when we're comparing different cars and each one has a different height above ground, even more accuracy is lost.

This is a perfect example of why bench racing is never accurate. Results of any one run are based on so many variables it's insane. Drag force varying between cars and getting even more complicated when winds are included. Driver skill, transmission type (shift speeds), gearing (number of shifts), power to weight, torque to weight, traction (in every gear), tires, it goes on and on.

http://media.caranddriver.com/files/...tory-final.pdf
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