Hi,
After installation of new tires, my left rear wheel alignment was off, 0.30 degrees, but Toyota who sold the tires and installed them, said, "Fo' getta' 'bout it." So when I had the first tire rotation, although not bad, there was a slight, asymmetry wear, 0.77-0.78.
I bought the Firestone "life-time" warranty and decided to fix the problem with a shim kit. A shim kit consists of a set of metal tabs:
1/128
1/64
1/32
1/16
1/8
The problem is there are no guidelines on how much correction each set of tabs provides. Installing the shims is about as difficult as changing a tire with four bolts on the wheel assembly to loosen and torque-tighten. I have an NHW11, 2001-2003 Prius and after multiple visits, this is what I found:
Toe (horizontal adjustment):
1/32 ~= 0.60 degree (0.30 -> 0.90)
1/64 ~= 0.30 degree (0.30 -> 0.01)
Camber (vertical adjustment):
1/16 ~= 1.7 degree (2.0 -> 0.3)
1/32 ~= 1 degree (2.0 -> 1.0)
The Firestone alignment systems, two separate shops, agree that the car is right in spec. However, I'll be doing some high-speed, temperature profile tests to further tweak the numbers.
My goal is to have an even temperature profile across all five treads for all four wheels. This should minimize local stress for longer tire wear and hopefully, the lowest possible drag. I'll then take the car back for one more "baseline" measurement and be done with it.
Bob Wilson