What causes rear tire cupping? Nitto g2 555s

[Metz3020827]

Hi guys! I have been having vibration issues in my seat and the floorboard of my car so I thought my tires were out of balance. I took my 17 Gt to get the tires rebalanced at discount today abs they showed me that the rear tires are cupped quite a bit, probably resulting in the vibration I’m experiencing.
There appears to be a humming noise coming from the tires too.
What is the cause of it? My shocks aren’t leaking and it looks like the suspension is in decent shape.
They’re nitto g2 555s 305/35r19 on a 19x11 wheel. They’re directional so they’ve never been rotated and they’re down to the wear bars now after 16 months.
I have -2.7° of camber bc I don’t have camber arms and I’m lowered. Is it bc lack of rotation and my alignment ? Do I need to worry it might be something else?

I’m getting new set of nitto g2 555s tomorrow from discount so no issue there I just want to make sure I’m not going to have the same issue.

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[SheepDog]

Generally, Out of spec Toe angles are the primary cause for cupping. Did you get an alignment after lowering it?

 

[Metz3020827]

Generally, Out of spec Toe angles are the primary cause for cupping. Did you get an alignment after lowering it?

I have had multiple alignments since owning the car, and the car was already on coilovers when I got the car 2 years ago. I’m tempted to buy rear camber arms and go take it in for the alignment. It’s $770 for these two tires with install. I bought them last February.

 

[K4fxd]

Why do you need camber arms? Are you at the max factory adjustment?

Worn shocks will cause cupping too.

 

[Metz3020827]

Why do you need camber arms? Are you at the max factory adjustment?

Worn shocks will cause cupping too.

The shocks aren’t leaking and they aren’t making any sort of clunking noises. How would I know if they’re bad?

 

[K4fxd]

How would I know if they’re bad?

The old bounce test is one way.

 

[Metz3020827]

The old bounce test is one way.

Car doesn’t do anything when I press down on it

 

[K4fxd]

Car doesn’t do anything when I press down on it

In that case you would have to take them off the car and see if they still damp. Are they true coil overs or are they divorced spring? Is the coil on the shock itself?

Do you know how many miles are on them?

Check your rear hub bearings these are known to go bad.
Some tires just cup at the end of their life.

 

[robvas]

Unbolt the shock and see if it extends or push it in and see if it extends back out

 

[saleen367]

Have them check wheel bearings when you do an alignment.

 

[Metz3020827]

In that case you would have to take them off the car and see if they still damp. Are they true coil overs or are they divorced spring? Is the coil on the shock itself?

Do you know how many miles are on them?

Check your rear hub bearings these are known to go bad.
Some tires just cup at the end of their life.

They’re fortune auto coilovers. I’ve had the car for 27k miles and they were on the car before. I’m not sure when they were put on

 

[K4fxd]

Just have to start checking things. I've never used that brand but google says they are pretty good. I'd remove the rears and send them in to get rebuilt. I have found most street shocks last about 50K, start subtracting miles for hard use.

Check everything mentioned in this thread.

 

[Metz3020827]

Just have to start checking things. I've never used that brand but google says they are pretty good. I'd remove the rears and send them in to get rebuilt. I have found most street shocks last about 50K, start subtracting miles for hard use.

Check everything mentioned in this thread.

So me and my pops took my wheels off and checked everything. The tires are worn on the inside on both tires and both cupped on the inside on each side in the rear. The passenger side camber is a little worse and the cupping was also worse. I’m going to chalk it up to them not being rotated and being worn down where they are as the culprit for now. I am getting my new nitto g2s tomorrow.

 

[K4fxd]

You are running a lot of rear camber. I'd drop it to -1.75. I never liked the feel of 2 or more negative rear camber.

 

[Cheatham]

Camber and toe, I put the same tires on as yours and reset my camber to as close to 0 as I could and had to reset rear toe as well, it can be done with the factory components.

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