Weird Tire Wear

fj12ryder wrote:

Kjun wrote:
Cupping dual wheel tires is nothing new. when it starts there is no straightening it out. Most causes out of balance, bad shock ,lack of rotation. Tire rotation, inside rear to front, front to rear outside, outside rear to inside rear. If tires are directional move side to side also. If different rims remount.

Why would you move directional tires side to side? Directional means they're designed to rotate one direction. Moving them to the other side would go against the directional design.

You can move directional tires side to side but you'd have to dismount the tires and flip them. That said, directional tires run fine backwards. They are just designed with superior traction in one direction. Mfg don't make tires that blow up if run backwards.....except maybe Firestone, lol.
That said we are talking about HD pickups, of which there are precious few directional tires available unless you're running low pro tires designed more for LD trucks and SUVs.
I've never seen rear tires cup like the OP describes, single or dually. Never seen them cup at all. Rotating to the rear straightens out bad tread wear patterns. Never put a bunch of miles on a truck so far out of balance of broken cords to see that effect either.
But doesn't seem like the OPs problem. New truck no vibration.
But you did have the tires rotated. I'd say the most likely cause is those were the front tires 7k mi ago and you're just seeing them now on the rear.
You can tell if they're actively cupping or feathering by feeling the tread. If the feather edges are "sharp" then it's happening now. If they are dull/ rounded off a bit then it probably happened on the front and is slowly wearing back to flat tread. Which will take longer on an unloaded dually (not much towing the camper in the winter?) than a srw with 2x the weight on each rear tire or loaded up.