The one thats on it??
It's a 32, but Idk if you can fit a 33 w/o rubbin. If you get a 2.5" you can fit 35's on stock rims though!
2006 F150 Lariat SuperCrew 6.5ft bed, 4x4, 5.4L, 3.73LS rear, G-Force True Ram Air Hood, Zone 4" Suspension Lift, ATX Artillery Chrome Rims 18x9, Cooper STT Tek3 325/60R18, Westin Ultimate Bull Bar 3" Chrome, Edge Evolution Power Programmer, Custom Side-exit Exhaust with Dynomax VT muffler, plenty of Chrome and Custom Stainless Steel Accents! My Mod Thread Confused about Tire Sizes?! How Much Air Pressure Do I Need?