don't guess by law every tire has recommended psi, load rateing, date of manufacture and as everyone will remember ford explorer/firestone. The trailer tire is the weakest link on the trailer since they often don't get any attention. Under inflation causes heat, heat causes failure. Read the side wall of the tire and take a psi reading when the tires are "cold" as after even a short use psi can increase by 10 psi. Also while looking at the side wall ck out the load rating which when mutilplied by each tire will give you the capcity of the trailer. This is really important.