Originally Posted by 1963tradewin
The 5200lb axle is a Dexter Torflex. I replaced the original in 07. The frame has surface rust, but looks solid.
It sounds like that is the perfect axle for that trailer. If it has a 4" standard structural channel frame (that is in good condition) it should be fine when the added strength of the shell is added to it. For an equipment trailer, with no shell, I would have used 5" structural channel.
All frames flex, but if built properly they are very rigid.
There is a point where counting on the shell to give a significant amount of the structural integrity is counter productive. If the shell is in good condition and attached properly it is fine, but when they get old and come loose it can create problems. Keep in mind the amount of weight that the manufacturer is saving is minimal.
The weight of standard structural channel is as follows:
3" 4.1 #/'
4" 5.4 #/'
5" 6.7 #/'
6" 8.2 #/'
If a trailer was 20' long, including the tongue (40' of material) the weight difference between a 4" channel trailer and a 5" channel trailer is only 52#. This doesn't include the upsizing of the cross members on increased size on an axle. Airsteam could upsize their frame on their single axle trailers from a 3" channel to a 5" channel and put a 5,200 axle on it and only increase the dry weight by about 150#. The carrying capacity would increase 550# and the frame would be strong enough that you could lift it from many more locations. The frame would still flex, but not as easily. That 5" frame would probably take a 6,000# axle.