Reversing cupping.

I bought a used set of Cooper S/T Maxx tires I was told have about 8k on them. They came off of a 5th gen T4R. I don't know if it had suspension issues, but these tires are cupped a little more than I realized when I bought them. At first they drove smooth up to about 55mph. As I've been driving more, they are smoothing out at higher speeds. Sometimes they do cause to teeth rattling vibrations at certain speeds, usually around 65mph. Yesterday, they were completely smooth at 80mph.

Anyone else been able to completely reverse this, or will I always have a vibration at certain speeds? If it was a balance issue, the vibes would always get worse at faster speeds, right?

 

Rotate them diagonally, reversing the tread direction helps a lot.

 

My original set of Maxx's were quiet before I rotated diagonally, as before I always did front to back only. They still rode smooth, but they didn't sound it anymore.

 

You can kind of tell how the tires are with the layer of salt on the tread.

 

Looking at your pics, I see what you mean about that layer of salt... But, what does it mean? What would cause that? Is it supposed to be like that? What can you do not to make it worse - is frequent rotation enough? Yeah, I know... Bunch of silly questions... (Almost belonging in turd gen forum)

EDIT: my questions we're not aimed directly at OP...
After pondering about it a little bit, would wrong toe-in cause this cupping?

 

https://youtu.be/GAasIWzUJaU
if you can find a tire shop that does this, it's exactly what needs to be done.
No amount of balancing can fix tires that are not round.

 

Is this a common service?

 

Common, maybe not. You likely won't find them at big box tire stores.

Easy to find in an actual tire specialty shop, yes, it should be.