Quick call to Hoosier East says my 18105 tire is 2 ply! And he says ALL there front runners are 2 ply. Havent had a problem. BTW I do not run inner tubes on the front.
The load rating for the tire should be right on the sidewall so you can see what they are rated for. IIRC, the M/T Sportsman 8-plys I have hold 60 psi pressure.