Tires: rear tire cupping issue, rear wheel bearings, alignment specs

Question
The last two sets of tires on my Subaru (now with 150K miles) had cupping on
the right rear tire. The dealer recently replaced the right rear wheel bearings,
which were noisy. The right rear camber is out of spec (-2 degrees, spec is
-1.3), presumably due to a previous accident, and is not adjustable by normal
means. The right rear toe was also out of spec but was corrected. The dealer
thinks the rear struts might need to be replaced, but there is no other
evidence of strut problems (leaks or bounce test). Could the camber problem
cause cupping, and if so, can it be fixed? Would it be a good idea to replace
the struts? I got 66K on my last set of tires, so it would take a long time to
amortize any repair expenses by improving tire lifetimes.

Answer
Alan,

It is more likely that the toe is what was causing the cupping than the strut.

Alignment specs - For some reason, most alignment specs are too wide.  Every time I try to trace down a tire wear problem and can verify the actual alignment settings, either the alignment is "out of spec" or the alignment is in the outer half of the tolerance.  I interpret this to mean the alignment specs are twice as wide as they should be.

And, of course, once a tire develops a wear problem from alignment, fixing the alignment doesn't fix the tire wear - the tire is already worn and you can't add rubber back onto the tire.

But you ought to fix the camber while you are working on this problem.

Let me put it this way - just because there isn't a built in adjustment doesn't mean the alignment can't be adjusted.  It might mean an eccentric bolt or slotting a hole, or in extreme cases bending the vehicle's structure, but every suspension can be brought into alignment.

So find yourself an alignment shop that agrees with me - they are the true professionals and not restrained by "conventional wisdom".

Hope this helps.