I'm not sure if it's the same for all tire suppliers and tire ratios. I have Falken tires and their maximum for 9" wheels is 275.
2014 GT Premium, Custom Painted, 401A, MGW, Brembo, Steeda CAI & 93 Tune
Steeda Sports, HD Mount Koni STR.T BMR Rod/Poly adj. LCA & Relos, PHB & Bracket
Forgestar Custom Painted CF10 19x9+35 & 19x11+42 Roush Grilles & Chin Splitter
FRPP Quad Axleback 3dCarbon GT500 Spoiler MMD Window Louvers SHR Fuel Door JLT Oil Sep.