Need more details about your car? Not sure what size rims you have or if your fenders are rolled? I think you can go as big as 245/60/15 if you have stock rear suspension. But I don't think anybody makes a Drag Radial/Slick.
I am running 235/60/15 BFG Drag Radials on my car currently with stock rear suspension & KYB rear shocks.
__________________ 1966 Mustang Coupe
Ford Racing 5.0 HO Motor(Crate)/B303 cam/1.7 RR
TFS TW Heads/Edelbrock Perfor RPM/Holley 650 DP
Mallory Dist/MSD Blaster/Holley Electric Fuel Pump
2.5" Exh H pipe/Flowmasters 40's/Dr.Gas Tailpipes
Lakewood T/A Bars/Aluminum Drive Shaft + loop
Auburn 3.55's/SSBC disc's/C-4 wTCI 2800 stall
Fiberglass hood/trunk/bumpers!(100% Sicilian) | 
Adding slicks to my 1964 Mustang 
