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Hi,
Cupping is usually caused by one or more of several factors such as: An unbalanced tire, faulty wheel bearings, loose suspension parts, fatigued or worn springs or shock absorbers.
Diagonal scuffing and cupping across the tread face on rear tires indicates possible problems with toe. Diagonal tread wear on rear tires is caused when the direction the vehicle's wheels are pointing are not in line with the geometric center line of the vehicle. When this occurs, front-wheel steering can be affected and lead to tire slip or loss of traction or control. The wear pattern that develops on rear tires from improper toe will vary depending on tread design. Wear patterns from rear-wheel misalignment may resemble cupping on tires with performance tread design and diagonal scuffing on tires with an all season tread pattern.
I would start by looking for Tire imbalance. Have the Tires Dynamically or Road Balanced using a Hunter 97XX machine. In spect the Shocks for leaks and problems with rebound (press and release car and motion should stop within 2.5 cycles). Get a realignment from a pro like a Race Shop, not some Tire Store paying particular attention to the Toe settings. Assuming the Tires are OEM, they're shortly due for replacement (as much for age as wear), so saving them may not be possible. But, be sure to do these adjustments/checks before installing a new set of fre$h rubber. Hope this helps...
Happy Motoring!... Jim'99
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