Front Tire Wear Pattern - '99, 320k

[Neuner]

Had a newer odd vibration in my wife's '99 but I don't drive it often enough to notice at what conditions it occurs, so I had her take it to get the tires balanced and rotated.

They said the front tires have an "Up and down pattern with choppy thread" but it's minor. They are Cooper Discoverer ATP's with 30k miles on them.

She took a pic but I don't think I see what they are referring to. I'll have to look at home.

Is this pattern and chop typical for the front and what is the culprit?

 

[OEMGUY0720]

aka Cupping wear. Cupping is usually caused by excessive vibration from the suspension or steering or drivetrain system. I would start with your upper and lower ball joints, struts.

 

[TahoeZ]

Other possible causes: incorrect tire pressure; steering rack bushing wear; bearings worn or not torqued properly.