Tires cupping/feathering?

I've noticed for a while that my 2 rear tires are cupping/feathering (not too sure which term is correct) on only the inside of the tire. I think it's cupping because the surface is not smooth when I run my hand through the tread. The thing is, the tire has a lot of treadlife left and no visible camber wear even though I'm running about -2.6. After researching a bit, I noticed many makes/models of cars and even motorcycles also have this problem.

I'm running Falken FK452 but this happened to my 2 rear Kumho tires that I previously had before too.

Possible Causes?
1) Worn shocks - my Tein SS are old and is wearing out but I push down the trunk on each side to check if it bounces and it only rebounds once so I assume that they are still OK at best.
2) Teins have such soft spring rates, which leads to a lot of bouncing on the road, could this be why also?
3) Camber/toe issue?

What else can cause this or are my coilovers most likely the cause?
Has anyone experienced this that can chime in?

Here's a pic I found online that looks almost exactly like my problem.

I have idea what your taking about lol
the pik of the wheel looks fine to me

but then again ima noob

Uh .. does that mean that your shock is going bad ? I'm not too sure

Grab the wheel and try to move it forward or backwards, left and right. Most likely bad bushings somwhere. Bad shocks cause the middle of the tire to wear first.

I know what your talking about. You usually see cupping/feathering (both terms are different) wear on lifted trucks. I don't however know what it's caused by.

http://www.procarcare.com/includes/content/resourcecenter/encyclopedia/ch25/25readtirewear.html

O wow same thing is happen to my right rear tire

I see this a lot. Most likely alignment camber/toe is off. Get that checked out and that will fix your problem.

Thanks guys, I'll keep every input in mind.

Do any of you guys recommend "flipping" a directional tire? Meaning getting a wheel and simply unmounting the tire, turning it around, mount it back on the wheel, and switch sides?

I heard it's okay for dry conditions but bad in the rain if my tire is symmetrical-directional.

i do that all the time, i have directional tires so i flip flop them all the time since i have so much camber and the tire gets worn down faster on the edge.

Your camber could be off and you might have worn struts or a combination of struts/springs. Unbalanced tires is another one . Id say check all your bushings, tie rods etc. anything suspension oriented. If all that checks out id lean towards your strut. Bad camber would wear the inside out smooth. Cupping is normally caused from too much bounce in the tire.

Good Info
http://askville.amazon.com/tire-cupping-struts/AnswerViewer.do?requestId=690811