It's different for the front and rear. My F350 will trip the light around 65-66 on the rears. Recommended is 80 PSI even if unloaded which makes for a rough ride. The front trips at around 55 on mine. Recommended is 60 on the front. I am now running a Live Wire Tuner which has the ability to adjust these numbers and keep the light off. I run my rears around 60 unless I'm towing 5th wheel..then its up to 80. My fronts run at 65-70 all the time. Not sure what the F250 recommended psi is. Its on your drivers door. The light trips when you get 12-15 off that on the rears and 5-10 off on the fronts. My SRW F350 behaved like the DRW truck I have now.
It is my understanding that the threshold for the TPMS sensors is set at 75% of the recommended 65 psi front and 80 psi rear pressures (F-350). I like to run my rears lower than my fronts when unloaded so I retrained the system and told it that the fronts were in the rear and the rears in the front. I aired down to 80% of recommended which puts me at 64 psi for the front tires and 52 psi for the rears.