Rear wheel alignment - 07 Toyota Sienna

I have an '07 Toyota Sienna (2 wh drive) with 73000 miles. My first set of tires (OEM) were Michilins and when they needed replacement at 55,000 mi the 4 tires were worn very flat and even (thanks to regular tire rotation and frequent pressure checking). We replaced all 4 of them with Cooper CS4 Touring 225/06R17 M+5 and in the ensuing 18000 miles the rear tires show a wavy but regular wear pattern along the outside 1/6 th of the tread width and a constant diameter decrease of approx 1 inch width and 3/16" depth along the inside of the right rear tire. The left rear has the same constant diameter indentation along the outside 1/6th of the tire. (We forgot to rotate them!). The alignment shop says there is no way to adjust the rear axle to solve this problem, even though they showed me a picture in a catalog of after-market shims especially for the Sienna, and copied a page out of an adjustment specifications manual that show specific caster and toe-in adjustment figures for the rear end and gave me a printout showing my rear geometry is within tolerance.

They say it would do very little good to add the shims but I could add them if I want to. (…as if I could burn money trying to fix the unfix-able). They are blaming the tire tread configuration of the Coopers as being susceptible to “conification” which they define as road crowning naturally causing this problem. (but not on the Michilins?)

Got any suggestions?

Go to another shop that really specializes in alignments and have them get every alignment angle within spec using shims. Unless something is bent, it is almost always possible, although difficult, to get a vehicle perfectly aligned. Replace the now irreversibly damaged tires before you get a real alignment, and don’t forget to rotate them.

Irregular wear 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.

You need to find another shop.

Plus you need to be aware that you are NOT going to fix tires that already have irregular wear. The best you can hope for is to rotate the tire to a different position and perhaps the old wear pattern will be erased by a new one - but it’s possible that the tires are too far gone.