You will get more traction with more side wall going to a 16" or 17" wheel even @ 275 width. Stock rear suspension is not helping you either. Get SPL Spherical Bearings for your knuckles, adjustable upper control arms & there are a couple other things that can greatly increase your traction if you are willing to go further.
~Induetime~ "Lag Less" First Stock Turbo to break 500WHP on boost alone (Pre-E85). New track car project "Diseaze": http://arizonazproject.wordpress DOT com Custom fabrication for the Z32: search QFAB on Facebook: QFAB More custom fabrication: search FuturFabrication on Facebook: Future Fab