My neighbor loaded dirt onto one of those little 4x6 atv trailers with his tractor, and blew both tires. Just based on the size of the pile (~ 1 yard or so), I am guessing it was a good 1.2-1.5 tons. He had figured he ran over something since it was a construction site, but it had to be weight.
I've seen similar trailers with the tires blown at the local garden center that sells mulch, dirt, and stone. Too many owners are ignorant about the capacity of those trailers, and I guess the loader guy doesn't care. The stone yard near me is a little more strict, and won't load onto anything that looks sketchy -- I bet they learned the hard way that busted down trailers will put a dent into productivity if the scale gets blocked. They also require trailers have a rear gate of some sort. That is a pain for me, as most times I don't want the large mesh gate on my 7x16 trailer when I am getting bulk materials, so I plan to build a smaller wood gate at some point.