The winter tires that came with my Fiesta were all cracking at the tread despite being only 2-3 years old. Weird. What I found was one tire was at 29 PSI, one at 32, one at 44 PSI, the fourth at 62.5 PSI. This is after sitting in bags since spring I'm guessing.
Also, don't inflate your tires more than the maximum recommended on the sidewall door jamb sticker unless they're warm. You're just eating away at the centre of the tire faster than the shoulders. Cold at the noted PSI, warm maybe +1 or 2. No more no less.