stubert58

I'm riding a Trek 520 Disc with stock Bontrager H1 Hard-case Ultimate, 700x38c tires. The inscription on the tires recommends inflating to 60-90 PSI. I'm 6' ~220 pounds, and riding with no load. So my questions are:

1. What are the variables that determine what pressure you should inflate tires to?
2. I've read in a few places that the front tire should be ~10 PSI less than back, what is the reasoning for that, and do you recommend doing it?
3. Pressure recommendations for my situation?

Thanks!