i have a 92 lude with 4ws. the stock 15X(I think)6.5 rims are crap. looking into something larger, will this throw anything off?

 

Larger wheels will not throw you off, provided you stay with a wheel tire combo that's very nearly the same total outside diameter. Proper plus sizes take this into account and generate a proper tire size for the selected wheel size. So for a +1(16") size you'd have something near a 45 series(profile) tire. +2(17") size would be around a 40 series. You can get proper + sizing from tirerack.com or a tire size calculator like this one:

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