Quote:
Originally Posted by Diesel4me
Shimmy is caused by unbalanced front tires.  Either a balance weight has fallen off, or they were not balanced right to begin with, or tire wear has caused the tire to go out of balance. A bent rim can also cause shimmy.
Shimmy is always caused by rotating mass (front wheel(s)) being out of balance. |
Not always.
The excitation force comes from the wheel unbalance. A wheel is never "perfectly balanced" It's impossible. However, the residual unbalance in the wheel is usually acceptable and is not transmitted to the driver if all the remaining suspension components are in proper condition.
If an LCA bushing is severely worn, as an example, it will allow significantly more motion of the wheel and the response from the small excitation in the wheel will be magnified greatly.
This can also occur if the tie rods are shot. The wheel is then free to occilate around an axis through the ball joints. Shimmy can be the result.