Glad I found this thread. I just replaced a 13.6-28 tire and tube on my David Brown 780, yesterday. It took 30 PSI to get the bead to set with plenty of tire lube. But as was mentioned here the sidewall information didn't give a recommended PSI. My owners manual says 12 PSI for general work and 14 PSI for highway. I left 20 PSI in it last night and have adjusted to the 12 PSI today all is working well. :thumbsup: