About how many seconds could i expect to gain for the worse w/ a larger diameter wheel? Would it be a REAL noticable lag in acceleration? I'd go from a 205/55/r15 to a 205/45/r17 instead of the normal 205/40/r17. And a larger diameter wheel would take away from the fender gap right? THanks

*oh this is on a 4th gen lude

You can calculate the difference. But your speedo and odometer would be off by alot with that setup.

Use this chart to calculate differences in wheel & tire combos:

http://www.miata.net/garage/tirecalc.html