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      04-28-2012, 09:30 PM   #55
turb0mik3's Avatar

Drives: E90 335i Racecar
Join Date: Jan 2010
Location: San Diego, CA

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2010 BMW 335i  [4.45]
Good explanation regarding the downforce and drag, but I am talking about downforce in different directions as well. I am trying to wrap my brain around how you produce "downforce" from an undercarriage during extreme braking or highly banked (or not-banked curves). I sort of understand the pressure points as you stated, but might need some clarification. I would assume most of the undercarriage stuff is to reduce the drag, but I don't know how making the bottom of the car super slick and the back creates downforce, that just seems not logical. I do know that the rear diffuser literally "pulls" air out from under the car, but I think that would be a rather large drag reducer. Yes, the front splitter is making downforce but the underside of the car doesn't seem to produce a lot downforce and the rear diffuser (which is nice and I will have one soon) seems like it wouldn't at all either, only help with drag. Perhaps there is a correlation to when you reduce drag it converts into some form of downforce?

I have another question for you as well. You may be able to computer simulate the drag effects and what not of your underbody carriage and rear diffuser, but most of the wings and their drag is almost minuscule to the effect of cornering and braking capabilities. I shaved 5 seconds off a lap time with JUST adding the wing (I had a front splitter before that). I would increase my speed around certain corners by almost 6-7mph. I lost 5mph down a straight at 145mph and yes that does cost time, but two things 1) What % of most tracks are straight vs. turns 2) the amount of time you gain in braking is 5x more important than the 1 second you add from loosing 5-10mph (if that). Also, as you probably know, you can change the angle of attack on almost every wing. My APR wing is almost always at neutral position, so the amount of drag is not that much. I have been experimenting and even find to have a slightly greater angle of attack is beneficial to not having any wing at all. Most of the cars in the BMW CCA/NASA and what not have wings because of this importance.

I think you have done a great service to us with the testing and I am going to be doing the exact same thing to my car in the upcoming month. I just think you should go to the track and post a time with the current setup and THINK about getting a wing and seeing the difference.

Once again great discussion, but I just think the amount of drag you are talking about is so minuscule compared to the effect around corners and braking.

^^^ I think that is the perfect setup IMO.

Just reread, I paid 1400 for my APR 67"er. :-)

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