The stock tire size for a Ford F-150 is 265/65R18. This varies based on the specific model and year of the truck.
P235-75r15
WHAT IS THE TIRE SIZE ON 1953 FORD 100
235 x 75 R15
P235/75R15
P235/70R16
Ford 2000 Tire Size Ranger 2wd XLT with a 225/70R15 tire.
Most common tire size for a Ford F150 is 275/65-18, but check your vehicle manual, and look up tire size. Or if you don't have a vehicle manual, you can always call a local car dealership or a local tire shop, and ask them.
33.1250 33.1250
235/75/15
Stock tire sizes for the 1997 F150 were P235/70/R16, P255/70/R16, or 265/70/R17 ( I can't remember if the 17s were P-metric or LTs)
Stock Tire Size 215/75-15
The stock tire size is probably on the driver's door placard (assuming it is original door).