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      05-21-2010, 11:18 AM   #33
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Drives: MY11 E92 M3 Coupe
Join Date: Apr 2010
Location: İstanbul

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Originally Posted by gr8000 View Post
The figures posted are an approximation of the true speed i.e. the 302km/h is my "desktop" approximation of the true top speed of a 6MT M3 (assuming no electronic speed limiter). Here is my methodology:

First I calculated the theoretical top speed following this:

The theoretical top speed for the M3 I came up with based on the above (assuming 19" 265/35 tyre) is 315.4km/h for the 6MT and 335.4 for the DCT.

Then what I have done is to apply a 15% "tyre distorition factor" (which basically is a manual factor adjusting for tyre compression at higher speeds) in order to come to an approximated true top speed. The 15% figure came by comparing my theoretical speeds at redline for each gear of the DCT versus the actually measured true speeds for a stock DCT as these were measured by GPS equipment from a reliable Greek auto magazine. I was happy to see that my 15% correction factor was uniform accross all DCT gears and yielded the same true speeds as those measured by the magazine.

Then I applied the empirical 15% distortion factor to all gears of the 6MT.

The true top speeds I came up with are 302.3km/h for the 6MT and $321.4 for the DCT (assuming no electronic limitation).
Interesting data
I was only refering to gear box - diff - tire diameter calculation..