Re: New wheels soon
www.rimsntires.com/specs.jsp - Start there. Compare prospective new sizes to what you have on the car now.
On an 8.5" wheel the tire manufacturers won't have you going any wider than 255.
'05 Stealth Grey CTS-V, 19x8.5/10" CCW T140s with Toyo Proxes T1 Sports (summer), black Team Dynamics ProRace 1.2 wheels with 275/35-18 R-compounds (track), Hyperblack Rota Torques (winter), KW Variant3s, V2 front brakes, Hotchkis rear sway bar, EPS cam, TEA-ported 243 heads, FAST92 intake w/LS2 TB, JBA Camaro/G8 1-3/4" shorty headers w/JBA cat pipes, Corsa exhaust, UUC motor and tranny mounts, UUC shifter, MAPerformance trailing arms, Specter cradle bushings, etc...