How to Tell When a Suspension Component is Failing?
 

My 2011 coupe, just under 80k, is rubbing terribly on the rear passenger tire. Like normal dips on the road are causing the tire to rub on the bumper bracket, which is shaving the tire (not good.) I know you can shave the bracket/cut it off, but Id rather keep the functioning bracket as it is intended for bumper support.

I suspect the rear shock or dampener is failing. I have noticed the car is floaty and is not as firm as it used to be. Even the girlfriend is noticing the boaty feeling from the passenger side. This is only happening on the rear passenger side and my car is properly aligned (assuming NTB didn't mess that up too).

I am running 285/35/20, but I have ran this size before without any issues, and would only rub if I hit a large bump at a considerable speed. Now I can't even back out of my driveway without rubbing badly.

Sounds like it's time for coils?

Wheel specs?
stock suspension?
lowered?

Rear tire specs are 10" +38

Yes stock suspension and I am not lowered. At least to my knowledge. I did buy the car with 40k 2 years ago, so who knows.

Probably a blown strut. Stock suspension with 10 +38 isnt that aggressive to rub on normal dips. Is that side sagging?

I measured both rear sides with a caliper from top of tire to bottom of fender and the driver side was a good 15mm+ higher than the passenger side. I'll have to check if my extended warranty will cover a strut.

Sounds like a failing shock. Replace the rears and fronts in pairs. Or all 4 if you've got the money.