[flybouy]

Interesting that you have 5 different tires with all the same load range (C) with varying air pressures listed. Here's just one of the issues with replacing one tire at a time, you loose track and don't know what you have or how old any one tire is. Did you buy this trailer with this variety of tires?

I'd recommend as others have stated replace all 5 with same size D rated tires of a quality brand and inflate to max cold pressure listed on sidewall. Start off with a good reputable brand and if the tire replacements are due to inferior tires then that will stop. If tire replacements are due to rubbing curbs then more driving experience or perhaps training is in order. Tires with C & D sidewall ratings are not very forgiving when it comes to sidewall impacts.