Looks like Iowa has pretty much the same weight laws as the NW.
So with the weight laws the same, one of our dump trucks and the TrailMax TRD-50 tri axle could carry its max weight of 50,000 lbs.
If you looked at the post I mentioned before I was carrying 40,000 lbs of 2'x2'x4' concrete blocks single height which were spread out a little over 2/3rds the length of the trailer. And I could have carried more weight because I was 11,000 lbs light on the truck tandems. Now with a piece of equipment the weight is usually more concentrated in a shorter space. We have hauled 320 size excavators for other people which weigh just under 50,000 lbs.
I don't have any complaints with this trailer and it tows like a dream as long as the load is balanced and a little front heavy. The problem most people have with their trailer being squirrely is that they try and put all the weight on the trailer and leave the tounge weight light. Theese type of trailers are designed to have the tounge and truck carry a good percentage of the load as long as the truck is set up for it, meaning the hitch mount can carry the weight and that the pintle hitch coupler is rated for the weight. Our pintle hitch coupler a Premier 2300 is rated at 20,000 lbs tounge weight and 100,000 lbs trailer weight.
Also as I mentioned in the other post don't get a short tri-axle, not enough room to move the load back and forth as needed to get a good balance. Our deck is 30 ft long, fixed 5 ft in the front and a 25 ft tilt. And as much as I usually like Trail King trailers having owned a few in the past, their 50 ton tri-axle is not that great. The problem is with the short length as it only has a 4 ft fixed front deck and a 20 ft tilt deck, so it is 6 ft shorter than a TrailMax and will also cause problems with total length weight rules or bridge law.
Here is a link to the truck weight laws in Iowa.
http://www.dot.state.ia.us/mvd/omve/truckguide.pdf