I've been given inconsistent information in this regard. FR reps have given me a range of 4200 to 4500 for this particular product line, but I don't believe them. The ground was full of sharp gravel at my walk through, so I didn't get a good look underneath at the axle sticker. When I get the trailer home, I'm going to crawl under it and get the SN and will call the manufacturer to confirm the actual rating.
When I was looking at a comparable trailer in Carson City, it had rims that were industrial in character and I thought I saw 6 lug nuts, but it turns out there are 5 on the actual trailer. Since it is a leaf spring configuration with what appears to be about a 3.5 inch round axle I assume it is adequate for the GVW of the trailer, but knowing FR, I' sure they give no extra capacity. Doing the math, with a 400 pound tongue weight and a 4300 GVW, I suspect the axle has about a 3900 lbs. capacity. I'd like to figure out a way to add some shock absorbers to lessen the potential bounce, but I'm not inclined to mess with the suspension unless the axle company sells the parts for such a modification. I don't want to void any warranties.
Without a cantilevered axle configuration, combined with leaf springs directly under the I-beam trailer chassis, and the fact that we tend to travel on the light side of the bring the kitchen sink along scale, I am going to focus my attention more on making some comfort and utility mods that won't add materially to the weight.