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      11-12-2012, 08:44 AM   #32
TDIwyse
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Drives: 2011 335d
Join Date: Aug 2012
Location: MidWest

Posts: 1,027
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Thanks.

I read many of your threads and watched this same video when trying to learn better ml techniques. Thanks for sharing that stuff.

The data I had collected practicing with launching on the Michelin Pilot Super Sports (after the first trip to the strip with lots of traction issues), and then comparing to the Hoosiers, is here with posts 79 and 83:

http://www.bimmerfest.com/forums/sho...=598240&page=4

Looking at the various GTech HP/rpm data in that thread it seemed obvious to me that the hp starts rolling off above ~ 4400/4500 rpm. And the HP curve is such that its nearly constant from ~3500-4400 which is about perfect for the gearing of the vehicle (the car seems to self shift at ~4600 brings you back down to ~3600 and at about the same power).

http://www.nittotire.com/Tire/nt555r#size

Looks like the NT555 in 275/40R17 are 25.6 in diameter, so theyre a little smaller than the 26.0 of the Hoosier 245/45R17.

Looking at my track recording (and pausing the playback at specific points) the car self initiated the 4/5 shift at ~4600 rpm just before entering the trap and the rpms fell to ~3600rpm (5th gear engaged) as the car was just passed the finish line. Using GPS data and rpms I had calculated 4600 rpm with the Hoosiers in 4th gear as being ~111mph. So with the 25.6 Nittos Id guess your car did the 4/5 shift at ~ 109 (circumference is proportional to diameter, so 111*25.6/26). Of course depending upon tire air pressures the difference could be more/less. I had my Hoosiers at 27psi for the run, which is pretty high.

Im inclined to think at this point the car has enough power to cause the 4/5 shift to occur during the run anyway, so it would be better to move to a lower diameter tire and gain some gearing advantage.

Anyone interested in a pair of slightly used Hoosier DOT 245/45R17s?
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