each pound less of unsprung weight has the effect of a 1hp increase as opposed to every 10 pounds of sprung weight has the effect of 1hp increase. of course if you add more, then you would have the effect of losing hp. when choosing tires sizes, you try to keep the diameter to be the same as the original so you wouldn't screw up your speedo reading.
323ci manual / bbs rk / toyo t1-s 225/45ZR17
i'm bored as hell!