I'm wondering, how much of a role does the ITR wing play on the car in terms of performance?

My first assumption had been that it was purely cosmetic for a more aggressive appearance but my friend tells me that it plays a small role...

Someone enlighten me please?

 

well from wat i know its to put a little down force on your rear wheels.

 

Check the recent "pics of wingless r's" thread for a practical explanation. Pay special attention to George Knighton's posts, since he is one of the few that has done actual on-track testing. Not lap times per say, but a good description of the car's handling with and without the wing.