Impact of "Good" vs "Perfect" alignment?

Now that my rear axle has been replaced, and I wore out two tires 100% due to the bad rear alignment...

...I am now seriously curious about the impact of "Good" vs "Great" alignment.

BACKGROUND

Toyota Factory Specs for Gen 3 have specific numbers for a "perfect" alignment, with acceptable variation. See below (my table is for 195/65R15 tires, and is from the service manual.)

We know a few generic things AFAIK:

• Front caster can't really be adjusted
• Front camber can be modified by changing special bolts
• Officially, rear camber and toe can't be adjusted. Change bent parts (eg I just replaced a rear axle.) HOWEVER, third party shims appear to make some (small) adjustments possible, particularly if one is careful to also shim the caliper mounts.

We also appear to know:

• Front caster affects steering
• Camber and toe affect tire wear to some extent
• Many like to have RF camber more negative for right-side-of-road driving (how negative I have no idea )

I also have observed on my own Prius: having rear toe and camber off by quite a bit, DID wear the rear tires down quite rapidly. From ok to flat and flat tire in a few thousand miles.)

HERE ARE MY QUESTIONS

• Is there any actual data relating imperfect/bad alignment to tire wear?
  • E.g. a great fact would be: for every 0.01° that Rear Toe is away from the "perfect" value, one loses about NNN miles of tire wear on average.
• Does anyone have anecdotal data on improving tire wear through...
  • Better alignment
  • Improved tire inflation (vs factory specs?)
  • Something else?

FWIW, we run 60-80k mile rated tires and have never hit even half the ratings...

(With my new axle, all of my alignment numbers are in-spec.)
- Front camber: -0.2° -0.6°
- Front Caster: 5.8° 5.4°
- Front Toe: 0.10° 0.09° (Total Toe 0.19°, steer ahead: 0.01°)
- Rear Camber: -1.2° -1.5°
- Rear Toe: 0.02° 0.17° (total toe 0.19°, thrust angle -0.08° )

I would apply known data to these "good" but not "perfect" numbers:
RF camber -0.6 (off by -0.4°, cross camber -0.4)
RF caster 5.4° ("off" by -0.5°, cross caster -0.4)
LR camber -1.2 (off by -0.3°, rear cross caster +0.3)
LR toe 0.02 (off by -0.12°)
RR toe 0.17° (off by +0.03°)

TOYOTA FACTORY SPECS (For discussion)
FRONT Unloaded
Camber: -0.22° +/- 0.75° and R-L difference 0.75° or less (0.53 to -0.97° range)
Caster 5.88° +/- 0.75° and R-L difference 0.75° or less (5.13 to 6.63° range)
(Note: OEM Front Camber bolts can adjust in 0.25° increments)
Toe: 0.10° +/- 0.10° (0 to 0.20° range)

REAR Unloaded
Camber: -1.48° +/- 0.50° and R-L difference 0.50° or less (-0.99 to -1.98° range)
Toe:0.14° +/- 0.15° and R-L difference 0.38° or less (-0.01° to 0.29° range)

(total toe 0.29° +/- 0.30°)
​

 

You'll find that saga elsewhere here. The TL;DR version: turns out that many small cars today have a solid beam rear axle. Reasonable performance and low cost... BUT: completely non-alignable. If you bump a curb a little too hard, you get to replace the entire axle!

I'm getting ready to post my how-to on replacing the rear axle.