I called Progressive and the tech support guy said they don't have a larger spring. Then he said the next size up was for a Harley Dyna that was 300lb per square inch. To hard for my need. Yes, he said the Dyna had a heavier payload then the Rocket. You take it from there.
Maybe you can get the Hagon people to build you something custom that's rated to haul 550-600 lbs or whatever the total comes to with the torquing force from the trailer.
My 444 HD's wound to about three rings work perfectly to haul 450 lbs or so, though, and were a noticeable upgrade from stock, but I guess I'm not shocked that 550+ and a trailer is too much.
Slidderhd,
In your situation I think I'd contact Hagon and talk to them about your needs. They seem to be pretty responsive to customer feedback regarding spring rates required.
I picked up a set of nearly new Showa air shocks (off a CVO Harley) at a swap meet a few weeks ago. Came off a HD Tourer model .. they are 12 inches long. Cost me $40 , thinking about giving them a go and see how they are.
I'm interested in the 444s, and looking on Amazon, I see "this will not fit your bike" . . . I don't trust software without a highly critical look first . . .
Might one of you knowledgeable folks chime in ? Buy these or not ?
They'll fit. There's a heavy duty and normal variants. The HD are good if you mostly travel 2-up (or are 250 lb+...), so if you're looking for the 2-up friendly variant you have the right one.