What are you trying to accomplish? Shims are the aftermarket repair parts industry's way of correcting a misaligned wheel when no other adjustment method is provided by the manufacturer. You don't just stick in some random shim. Those shims are selected and installed by the specialist while the car is on the alignment rack, after the mechanic has taken very precise readings, and he has calculated the amount of correction needed. Those shims are not do-it-yourself items.
There are a number of different styles and types of shims manufactured by different suppliers. The large plastic rings have a thicker area and a thin area. You install it to put the thicker side on top, bottom, front, or rear, depending on which way the wheel needs to go. They can also be installed mid way between those four positions to change toe and camber at the same time. The shim will come with a huge chart to show how to install it. With some designs you have to select the shim that provides the desired amount of change. Some shims are two-piece designs. The two halves can be rotated to adjust the amount of correction they provide.
Shims are only used on rear wheels and those are always adjusted first during the alignment. That will change the way the car steers, then the front wheels are adjusted last to match the rear wheels. The final adjustments are the "toe" on the two front wheels. That is extremely critical and must be precisely set to prevent tire wear. That can't be set correctly without having the car on the alignment machine.
Sunday, June 2nd, 2013 AT 11:27 AM