I run 18" simply because the tires and wheels are cheaper and the sidewall is more compliant on an 18" tire. Next time I will get the 305/45-18 vs the 305/35-18 I have now because of the height difference. The transmission sometimes gets confused because the wheel speed is different than the indicated speed and I don't have a tune to compensate for the tire swap.
'15 Z/28 #325 black a/c & stereo. 2:11 VIR Full 1:45.531 Summit Point Shenandoah Circuit
Advanced Induction cylinder heads & B-3 cam by Race Proven Motorsports...installed by me. 521/441.
'12 ZL1 10.52@131 1.55 60' 2:13 VIR Full (sold)