Seriously? Keep lowering pressure 5psi at a time until you start loosing tire beads... then add pressure to that number 1psi at a time until you stop loosing tire beads... then add a few psi for safety and wheel right on past the 90% of folks out there running WAYYYYyyyyyyyyyyyyyyyy too much pressure.
Only exception -- if you're running smaller tires and can't afford the clearance. If that's the case, get some bigger tires and enough lift or sawzall to fit 'em and then start reading this post again from the top.

Randii