Tires: Tires cupping on Toyota Corolla, firestone tires, 2005 toyota corolla

Question
My wife has a 2005 Toyota Corolla. She had Firestone tires put on the car last year and has had trouble since. The Toyota dealer says the car is okay, but the tires are Cupping. The tire shop says that it's the car (e.g. bad alignment, etc). Which do you think it is?

Answer
Donald,

Tires don't wear unevenly by themselves.  It caused by the way the vehicle uses them.

Irregular wear (incorrectly called cupping) is caused by misalignment and aggravated by insufficient inflation pressure and insufficient rotation practices.

It is my opinion that most vehicle manufacturer alignment tolerances are too wide by half.  The target value may be OK, but the published range of acceptable values is too wide.  I think the value needs to be within the inner half of the range.

My experience is that IF the vehicle's alignment is within the inner half of the tolerance, there aren't any tire tire wear issues.