Originally Posted by Oaklevel
That's really interesting. Esp if you took into account tongue weight.
On my trailer the GVWR is about 700lbs more than the combined load rating of the tires. If you don't take tongue weight into account, the tires are overloaded when the trailer is sitting in a parking lot.
My assumption of tongue weight may be a little bit light, but not enough to change the conclusion.
I also called Dexter who makes the Torflex axles on my trailer. I got through to an engineer who agreed that the axle force constants won't be exactly equal for each wheel. (The torsion axle relies on rubber to create its springiness.) He agreed that it wouldn't be unreasonable to assume that one tire might get 10% more weight than another. So even if everything else is perfect, one shouldn't assume equal loading on all four (or six) tires. The engineer was quick to also point out that trailers come out of the factory imbalanced, with more weight on one set of tires than on the other due to asymmetrical loads like slide outs. As far as I can tell, FR assumes equal loading on all tires.
Carlisle Tire recommends allowing a 20% margin between trailer weight and combined tire load rating. It's easy to understand why this makes sense because it would allow for the above effects without overloading the tires.