What causes "CUPPING" of tires?

Boggus · October 06, 2014, 04:08:59 PM

2013 SHO PP ... Driver rear tire is cupped fairly bad. Started out as a noise inside the cabin and thinking it was a bearing issue, I investigated. The inside edge of the tire is cupped or scalloped fairly bad. I am told the alignment is the cause but I don't understand how the alignment would scallop the tires, figured alignment would make an even wear around the tire, not cupped.

Here is what I have found on the net:

Along the Edge
Scalloping along one edge, typically the inner edge, tends to happen as a result of problems deeper in the suspension. Bad wheel bearings can cause edge scalloping, but so can bad ball joints, bad steering or sway-bar end links, damage to the steering linkage or control arm, and severely damaged suspension bushings. This kind of wear happens because something in the suspension is bouncing or vibrating when that wheel is compressed during cornering. Edge scalloping could be a sign of impending disaster, so have it checked out immediately.

A dealer looked at it and stated alignment... so post some thoughts please. Just the driver rear tire.

2013 SHO PP
Eibach Springs
Around 14K on the tires - Springs been on the car since about 1500 miles.

ZSHO · October 06, 2014, 04:15:51 PM

How many miles on the tires? and how long have you have the Eibach springs on?

SHOdded · October 06, 2014, 05:23:20 PM

Definitely check the shocks/struts. Very possible one or both are leaking. Wouldn't be the first case.

Boggus · October 06, 2014, 05:45:59 PM

Quote from: SHOdded on October 06, 2014, 05:23:20 PM
Definitely check the shocks/struts. Very possible one or both are leaking. Wouldn't be the first case.

So, there would be fluid (oil) leaking down the housing? I will check it later tonight.

IHeartGroceries · October 06, 2014, 06:30:01 PM

Blown suspension dampers.
But usually when it is to the point that it is cupping tires, the vehicle is noticeably boaty or bouncy.
Was likely already a pre condition to the springs. But perhaps exacerbated by them.

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Boggus · October 06, 2014, 06:36:40 PM

So... best way to tell? Car does not seem bouncy or boaty

wasinger3000 · October 06, 2014, 07:16:48 PM

You could jack up the body by the tire in question. Once the suspension is unloaded try to twist your wheel from side to side then top to bottom. See if anything is loose. Then try to see if the shock is bad.

Boggus · October 07, 2014, 09:38:09 AM

Tires are just about gone in terms of life, but this is the only one showing cupping and its pretty bad.

I jacked up the rear driver side and twisted side to side/up and down without any real movement. Now I can place both hands under that wheel/tire and push up and move the shock up and down some. Not sure on how normal this is but I am certainly no weightlifter!

Bad quality pics...phone is on its last leg.

ZSHO · October 07, 2014, 09:46:16 AM

Trying to help you out but unfortunetly you never responded to my question what tires do you have and how many miles.

Boggus · October 07, 2014, 09:53:38 AM

It was added to the original post after you asked.... atleast the mileage.

Goodyear F1 - Car has 27K miles (2nd set of F1)
Around 14K on the tires - Springs been on the car since about 1500 miles.

wasinger3000 · October 07, 2014, 09:59:13 AM

You can see the oil on the shock in both pictures. That's not normal. It must be leaking.

Boggus · October 07, 2014, 10:02:54 AM

So does this become an issue with beating a dead horse? I will check with the dealer and see what can become of it.

Eibach springs on the car (pointing the finger)

ZSHO · October 07, 2014, 10:15:07 AM

Quote from: wasinger3000 on October 07, 2014, 09:59:13 AM
You can see the oil on the shock in both pictures. That's not normal. It must be leaking.

The best way would be also to check the other side rear tire and check for leaks and if not that will be your answer,good luck.

SHOdded · October 07, 2014, 05:19:38 PM

Good luck with the dealer, Boggus! n8rfastback's SHO also had leaking rear shocks, not sure if he had lowering springs on at the time. Guessing the rear shocks are a weak point in the suspension compared to the fronts.

Boggus · October 07, 2014, 05:25:29 PM

Made an appointment, goes in tomorrow am. I took the car to them last July when the noise began to bug me and they told me it was due to a cupped tire. Never did they investigate any further as to the cause. So yesterday by brain worked and I started to see what the cause would be. Amazing. If it is the shock and they do decide the do the right thing and fix it...then we will address the tire issue as this caused the tire to wear prematurely even though they do need to be replaced as of now. I also looked at previous posts and see that I had a similar noise issue on the first set of tires...hmmm.