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      04-07-2007, 05:02 PM   #19
T Bone
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Originally Posted by swamp2 View Post
Tools such as this can do 30-60, 60-100 etc much more accurately than 0-X, the reason is is that wheelspin is required for the best time but of course just enough to get the momentum going and not so much to be loosing accelerative forces. This is extremely difficult to model and requires a myriad of factors such as weight distribution, suspension geometry, tire and pavement properties, etc., etc.

Air resistance scales with the square of velocity so at low speeds it is not so significant (even in 0-60) but for top speed it is one of the dominant factors. Leaving drag off because the software does not handle wheelsping is a fairly poor approximation that seems to give reasonable numbers but you are certainly "tuning" the software a bit to get an expected result. Here is the real question with similar aprroximations how close can you get to M5 or 335i times (I would not bother with Rs4 or Porsche times beacuse of the 4WD and rear engine effects which are quite large)?

For the M6, the model is pretty close after you plug in the data for SMG shift times, in fact, they look very much like the Car and Driver test. But as the time increases, the margin of error also increases.

For the M3, I left out drag simply because I couldn't find data, so if someone has the drag coefficient and front area, please post.

Here is a simulation of the M6 and a PDF of the M6 review from C&D....very close...

Aero forces really come into play after 70 mph, so while I left off drag for the M3, I think for the 1/4 mile this data is a good estimation since the software cannot model wheelspin.

If I left in drag with no wheelspin, the M3 would have done a 13.15 second quartermile and that would be heresy on this board and quite frankly would be wrong.

Wheel spin is big.
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"Aerodynamics are for people who cannot build engines"......Enzo Ferrari