I have 275/40 19 on mine on 19x9 wheels, my wheels are also a 42 offset.
You will need the steering rack stops also so the wheels don't rub.
2013 V6 MCoA, Performance Package, Security Package, Comfort Package and Electronic Package.
Mods OEM Backup Camera, BBK Shorties, FRPP Cut and Clamp X-Pipe, Borla Touring A/B's, Airaid CAI, Axle Xchange 2 piece aluminum Driveshaft, Koni Sport Shocks and Struts, Vogtland V6 Leveling springs, Ford Racing 302s wheels wrapped with Continental 275/40 19's, JBL GTO 8628 6X8 in all 4 corners. 2013 F 150 FX2 With a 6.2 Boss