I believe they are 8ply. Not totally positive but I think the owners manual says something like 25 or 30psi. If it is because they are just "stiff R4 tires" then my thing is, why would they(Titan I think) even make a tractor tire that? Can only use about 75% of the tread, if that. Id say on pavement that its less than that as the ground compresses a bit. Even with my 5ft brush mower hanging off the back and no loader on, the things are hard as a rock and perform the same way.