Weird Tire Wear

Cupping is not uncommon on dual tires.

Kuhn-thanks for the tire rotation procedure. My front tires are my newest ones, and I like to keep them fresh, so I like the idea of reversing your procedure. In other words-I'll mount some fresh tires on the left and right outer dual rims, then put those tires on the front. The old front tires then get moved to the inside duals on the same side. Finally the old left inside dual goes to the right outside dual and the old right inside dual goes to left outside dual. The old outer dual tires are then discarded.

OP - this technique would get your cupped tires off the truck sooner rather then later.

If I follow this procedure while replacing my front tires every two years my tires will get rotated out before they get too old and the front rubber will always be fresh.

Kjun wrote:
The left rear out side rotates the same direction as the right rear inside. The same for the right side. The rims are offset and can be used in any position. The tires are directional. If I remember right it would be something like this. (1) Left Rear inside to Left front. (2)Left Front to Right Rear outside. (3)Right Rear outside to Left Rear inside. (4)Right Rear inside to Right Front. (5) Right Front to Left Rear outside. (6)Left Rear outside to Right Rear inside.

Thanks, I never considered that the wheel offset on duallies changes the rotation of the tires. Thanks for the explanation.

Directional tires are usually for traction. This is controlled by tread pattern that gives them the ability to self clean. Some are directional by design at the job at hand. Off road, all terrain. highway mileage. winter / summer etc. Depending on the design is the way the tire cords are layered. Also the rubber compound. If it has a arrow on it make sure it is in the right direction what ever you have to do. If you want to see cupped duel rear tire visit your local truck stop or check out the 18 wheeler next to you in a rest area.

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.

The left rear out side rotates the same direction as the right rear inside. The same for the right side. The rims are offset and can be used in any position. The tires are directional. If I remember right it would be something like this. (1) Left Rear inside to Left front. (2)Left Front to Right Rear outside. (3)Right Rear outside to Left Rear inside. (4)Right Rear inside to Right Front. (5) Right Front to Left Rear outside. (6)Left Rear outside to Right Rear inside.

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.

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.

I am not sure how the rotation was done but it makes me suspicious. I do know the guy that wants to do it every 3k miles is nuts. At the prices they charge I could just buy a new set every 30k miles or so. If nothing mechanically wrong is found I think my best option is to get one more dismounted rotation and balance and if nothing is wrong with the tire just drive it and watch the results. In hindsight, I should have done what what the owner's manual says and that is just switch the fronts and rears from side to side. I let someone talk me into something that I didn't need.

Even though I don't think it is an issue I will check the lug nuts tomorrow.

I don't rotate my tires either, other than "flipping" the rear outer tires every 30,000 or so because the outside edge wears faster. I also swap the fronts side to side on occasion.

Cupping indicates something's moving that shouldn't be. Have you checked lugnut torque?!?

I would think you'd feel the vibration if things were out of balance.