Something you can do to determine the correct tire pressure.
Go get some carbon paper. Lay out a piece of paper put the carbon paper on it and another paper on it. Then slowly drive one of the cars tired over it. If all works out you will have an outline of the foot print of your tire. Deflate the tire some and do it again. At some point you will see no transfer in the center or no transfer on the outsides, what you are looking for is the widest uniform transfer.
There are other ways to do this, chalk is one way. Dampen the tire drive over paper, basically anything that will show the contact to the ground.
You might also be able to contact the tire manufacturer, give them the weight on the particular wheel and ask their recomendation
