I have those wheels in 18s and there is tons of room between the wheel and the brakes but this is what AMs site says........."Does not fit the Shelby GT500 or any Big Brake Kit equipped Mustangs". So yes you will need a spacer.
06 Satin Silver GT - Auto...ROUSH M90
PI 3k Stall, CAI, Afco Dual Fan HE, 4.10s,Trutrac, Detroit Rockers, Moroso, DSS DS, TCI Rachet Shifter, PA Deep Pan, Eibach Handling, FR P Springs, Strange Shocks/Struts, BMR, SS Lines/ EBC Rotors w/Reds, Mickey Thompson SC5, Nitto 255/305, Corbeau A4, Pypes LT's/H-Pipe, MBRP Resonators, Borla
2015 Sportsman Champion.