Shim kit and rear wheel alignment

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, asymmetrical wear pattern, 0.77-0.78. So 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:

1/64
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.

NOTE: You must have a torque wrench, 13 mm. socket, and torque it to 38 ft-lbs. It is absolutely necessary, a health and safety issue, that these bolts be torqued correctly.

Bob Wilson

 

<div class='quotetop'>QUOTE(mini2prius @ Jun 13 2007, 08:39 PM) [snapback]461275[/snapback]</div>

The kits cost about $20 and have enough shims for a dozen cars. I have a lot of left-over shims. Send me a PM with a mailing address and I'll send what you want. Once you get them, let me know how they work out and send me a couple of bucks.

NOTE: I only put pairs of shims on one side of the four-bolt attachments. This works because all four bolts can be tightened and the wheel is solidly attached. Use a pair of identical shims on one side to handle toe and identical shims on the other to handle camber. DO NOT use any single or diagonal shims because it would lead to 'rocking' and risk warping the wheel and axle plate.

Also, be sure to use a torque wrench to tighten the 13 mm bolts to 38 ft-lbs. This is not negotiable. Too tight and you weaken the bolts, they fall off and the wheel falls off. Too loose and vibration can back them out, the wheels go all cattywampus and if the bolt breaks, the wheel falls off. Did I mention using a torque wrench to tighten them to 38 ft-lbs?

Bob Wilson