I don't know if you already have the wheels and are sold on running the 15"s, but there is another straight forward option. I have drag raced my Z since the late 90s, and I have used the stock rear TT wheels with drag radials. Mickey Thompson makes an excellent drag radial in a 255/50/16 that is made of a soft compound used on their slicks. They will hook up at extremely high RPM launches with as much power as you can throw at them. I've used that tire for about 15 years, as have many local Z guys that drag race. Greg Dupree uses them in his Z that runs 9.30s. Hope that is of some help. As far as the 15"s go, if that is what you plan on using, give SpecialtyZ a call and ask for Jonathan, he's pretty knowledgable in regards to wheel sizes. Ph # 818 703-6272.