New tires should not be fully loaded or highly inflated because the steel bands in a new tire are all slightly different lengths and therefore some of them are bearing more tension than others. The steel bands in a used tire have been flexed and have stretched to the same length to bear forces evenly, making the tire MUCH stronger than a new tire. Inflate your tires to recommended specs for a few months and don't fully load them, to let the bands equalize, then increase your tire pressure, and payload.
I need two new tires this fall and will not be running my normal 50 lbs right off the bat.
Just my $.02 worth....