Hello all. I'm back from a long break of no RV'ing. (Moved, built a house, started working two jobs.) However, I can contribute a bit to this thread.
I have a 2001 Starcraft Gemini. Came from the factory with C rated ST175 x 80 x 13" tires. I knew nothing at the time it was purchased, about ST, LT or P tires. Tires, to me, were round rubber things. They held air, they got me where I was going (most of the time). Several years, and two sets of destroyed tires later, I got educated.
I DO check air pressure before every trip, during the trip, and before the return trip home. I DID travel at whatever the speed limit was. Tire history. Original tires (don't remember the brand), had about 3500 miles on them. Was on our second trip to Colorado from KY. Just outside of Denver had a blow out. It was Sunday and no tire stores open. Drove on to Utah with no spare sweating every mile! Next morning at a tire store, they looked at shredded tire but could not determine cause. Bought a set of C rated Tow Master tires. Now I had two spares! Those tires lasted maybe 5000 trouble free miles, and several years, then started showing signs of side wall checking. So I put a brand new set of HI-Run tires (purchased from etrailer.com complete with new rims) on before a trip out to Utah from KY. About 2600 miles. On the way home noticed a bad vibration from the camper and pulled off at a rest area. Could see nothing wrong and figured I had lost a wheel weight. I was 80 miles from home and went for it. Once home I found a hand sized piece of tread/sidewall missing from one of the tires! The other looked like it was about to throw a tread. Pulled those off and put the Tow Masters back on while I figured out what was happening.
I started researching and found out about the load limits and ratings on tires. Some quick math revealed that the C rated tires on my camper were too light. With everything loaded in the camper and TV a trip to the scales revealed the camper tires were overloaded about 150 lb each! My fault for not being better informed. Once I switched to D rated tires, (not easy to find a D rated tire in 13") I have had no trouble since.
I now have a new 2016 Venture Sonic 170VBH I will be picking up next weekend. It has dual axles and 4 14" load range C tires. Camper has a GVWR of 4000. C rated will hold 1360 each (5440 total)so I believe I am good. If I notice any issues I will go to a D rated tire.