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°)
Tire wear depends on the intent of design from the factory. The Prius specs are pretty tame. Ordinary amount of negative camber in the rear and a smidge of toe-in for the front. Not hard to push 40k tires to 50k. Of course, smoothness in acceleration/deceleration and cornering helps. As for tire PSI, the factory specs is low IMO, especially for the front. I set mine at 40-42 to get even wear. How did you manage to knock the rear axle out of alignment?
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.
