Agreeing with ZO- I'd add that you might be seeing affect of worn or failing control arm bushings - hell, even unloading of u-joints if exceeding their design range. Regardless of wheel size how do overall tire diameters compare old v. new?
\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear)
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HomeDepot pipe w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCAs, Airlift 1000, Monroe SS, PowerTrax No-Slip, and now CTS wheels with +1 rubber. Finally, wait for it... LT-4 knock sensor!