I have a spreadsheet with a formula that seems to work pretty well most of the time. I don't remember where I got the formula originally.
F/R PSI=(((153.6*W)*p)/(t^1.5785))-7.1685
W: rider+bike+gear weight in lbs.
p: Wheel load %
t: Tire width in mm
On my bike with 32s I run around 55 front and 65 rear