I expect that MTD may recommend an expecially low tire pressure on it's riding mowers to maximize the foot print of the tires and thereby minimize the pressure they exert on the ground below them. My understanding is that walking on grass after a heavy rain can kill the grass because the pressure exerted underfoot can compress the wet soil and drown the grass roots.

Every pneumatic tire I've ever had the pleasure of meeting face-to-face has always had a recommended inflation pressure or pressure range molded into it's sidewall. I'm surprised that thekmanrocks says that his tires don't have that information on them.