Originally Posted by Moflash
.......Under inflation will cause accelerated wear both inside and outside rib usually without cupping.Over inflation will cause accelerated wear in the middle of the tires tread.
Hope this helps.
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That part isn't quite right.
First, there are other things that have a greater affect than inflation pressure. For example, steer tires tend to wear on the shoulders and drive tires tend to wear in the center. So even properly inflated tires will show symptoms that most folks would view as over/under inflation.
Inflation pressure does affect cupping. It's kind of a multiplier - too low and the cupping gets worse. It's not a direct cause, but it does affect the results.