Wheel Alignment: Just how bad is bad?

Question

Context/Information: If I understand correctly, having a fixed axle in a car makes getting things aligned significantly harder. This seems to be the case in my 2009 Toyota Corolla and the rear axle. When my wife took it to Costco to get new tires, they told her the old front tires had some cupping and the rear set had feathering (don't have more details than that). She took it to get aligned, in order to prevent further unnecessary wear, and was told that the front was already within factory specs, and the rear was not adjustable (though the minor improvements to the front specs threw the rear left toe OUT OF factory specs and the left further out of spec for both toe and camber). The factory tires replaced had about 41,000 miles on them. The specs for the rear camber and toe are apparently -2.0 to -1.0 degrees and 0.01 to 0.26 degrees, respectively.

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Front Measurements

                         Before          |             After
                     Left  |    Right    |      Left     |    Right
Camber              -0.60  |    -0.80    |     -0.60     |    -0.80 
Caster               3.10  |     2.80    |      3.10     |     2.80 
Toe                  0.09  |    -0.02    |      0.00     |     0.01
SAI                 12.60  |    12.60    |     12.60     |    12.60
Included Angle      12.00  |    11.80    |     12.00     |    11.80
-------------------------------------------------------------------
                                         |           
Cross Camber              0.20           |           0.20
Cross Caster              0.30           |           0.30
Cross SAI                 0.00           |           0.00
Total Toe                 0.07           |           0.01

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Rear Measurements

                         Before          |             After
                     Left  |    Right    |      Left     |    Right
Camber              -1.20  |    -2.00*   |     -1.10     |    -2.10*
Toe                  0.21  |     0.01*   |      0.28*    |    -0.02*
-------------------------------------------------------------------
                                         |           
Cross Camber              0.80*          |           0.90*
Total Toe                 0.21           |           0.26
Thrust Angle              0.10           |           0.15


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All measurements are in degrees
* indicates not within manufacturer specifications

Finally, the shop stated The manufacturer does not specify rear CAMBER and TOE adjustments, leading me to believe the rear axle is solid.

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Question(s): How bad is a right toe reading of 0.28 degrees (0.02 above the spec range), a left toe reading of -0.02 degrees (0.03 below), and a left camber reading of -2.1 degrees (0.1 below)? my instinct is that this may reduce the life of the tires only very subtly, and would be mitigated fairly well by rotating tires. Is there a general rule to go by for alignment's affect on wear? How long SHOULD my tires have lasted?

Answer 1

You basically have 3 measurements in the front, and 2 in the back that are normally adjustable unless you have a solid axle (You don't). The front caster is adjusted at the strut mount, the front/rear camber and toe normally utilize rods to adjust. The toe utilizes the tie rods in the front that are attached to your steering box, and the rear usually uses a rear tie rod that is set in place. The camber is adjusted using a mounting arm in most cases, and all 5 of these should be available in your vehicle. There are of course other measurements that are looked at to determine whether your vehicle will drive straight or not, but these are the commonly adjustable ones. The numbers you mention seem small, and if the vehicle is not pulling, you should be ok. The most important thing to extend tire life is the pressure, if you let your pressures drop, you will wear the tire out. If they tried to align the vehicle, and it failed, you might need suspension parts at this point (pot holes are rod/arm killers). Most dealerships keep a competitive rate on alignments, so do not be afraid to call and get an alignment quote.

Answer 2

looks like they only gave you a 2 wheel alignment. Rear wasnt touched. I'd either go back or go elsewhere. There is too much variation across the rear wheels to run like that.