Update: I just improved my stock tires and rims and tires to 17 1/2" aluminum rims and load range H Sailuns, 215/75R17.5.
I did this after 2 of my stock aluminum rims broke....yes, broke. First one broke on my way home from San Diego where several spokes had full penetration cracks through them. Wheel mfg. replaced rim w/o charge. Then another broke last month on my way home from Orlando. I lost confidence in the stock Heartland supplied wheels and upgraded to better ones.
Photos are my new rims and tires, along with the 1st broken rim. I haven't photographed my other broken rim, but it was much worse than the one pictured.
My opinion: If you have rims on your trailer that match the one's I had that broke, replace them now and without hesitation. I talked to another Heartland owner with the same rims, which also broke.