Tires: choppy wear on tires?, target value, inflation pressure

Question
i just went to have my tires rotated and balanced and was told i have extremely choppy "bumpy" wear on my rear tires. i have noticed when i get above 45mph the car does shake quite a bit. i was told it more then likely is the shocks/struts going bad. could it be more then that? I'm planning to drive cross country in this car very soon and don't want to take off thinking it could be something else and not have it all repaired.

Answer
Heather,

You have irregular wear and that is caused by misalignment and aggravated by insufficient inflation pressure and insufficient rotation practices.

My experience says that the published alignment tolerances are too wide.  Not the target value, but the allowable deviation from that value.  I think it ought to be half of what is published.

Put another way, the alignment should be within the inner half of the spec.

You should be aware that even vehicles that do not have a pull can be out of alignment.  There are settings where one out of spec condition is offset by another out of spec condition – typically camber vs toe.