Pin weight is carried by tow vehicle so weight on trailer tires/axles should be less then max load rating of tires at max psi
GY Marathon 16" 'D'----3000# @65 psi (12,000# total)
GY Marathon 16" 'E'----3420# @80 psi (13,680# total)
2011 Montana should have come with 235/80R16E (3420#/each)
BUT RV tires are marginal especially IF:
Overloaded
Under-inflated
Run above speed ratings
Old (more then 5 yrs)
Changing to higher load rated tires is a good step....just remember wheels have to have same/higher load/psi ratings as the new tires
GY G614s ---good 'G' rated tire 110 psi-high dollar
Sailuns S637s have good reviews...again 110 psi-lower priced then GY