Just did lots of reading and posting questions on this same thing.
My 2014 Voltage came with Load E ST Akurett??? 3550 lbs. ( can't spell the tire but can spell JUNK) Found them online for 67 bucks and under 40 pounds!
I bought this rig lightly used and knew with a toyhauler with double 7 k axles I would most likely upgrade as I plan to put 20k kilometers on in the next 5 months.
Decided on the Sailun 637s and had 4 installed last Friday. Only towed to my storage facilty and leaving for Mexico for break so no real test yet.
4000 pound rating and 14 ply and coming in at 61 pounds each seems to be plenty for me but time will tell.
I think with the dual axles vs. the triple there is room for debate when choosing as the triple has more support and thus can get a E or G tire.
Found them here in Calgary if you need help locating let me know.
Good luck.