As you go up in tire class, just like TV classes, the tires of the same OEM/model/size will weigh more. Because they are made differently and are rated to carry more weight
If anyone has ever cut apart tires like I did while working through college (part time tire monkey, welder, mechanic, designer, etc). You'd have found that ST, Passenger & LT class tires has a safety bead on both the tire and wheel. Commercial class tires do NOT have a safety bead.
Commercial class tire side walls are thicker than the lower class. ST, P, and LT class sidewalls are in fractions of an inch thick. Commercial class sidewalls are normally over an inch thick.
Why said do NOT air down commercial class. Been there, done that...even after working in a high end tire shop for years...lost the seal on all four while aired down crossing a river bed up in the Idaho Panhandle...took me almost two days to hike out and another day finding someone who would drive me back up with the stuff to re-seat & air up
Suggest reading up and this is a good starting point:
RMA, Replacement Guidelines for Passenger and Light Truck Tires
