[Andy Baker]

Another thing to consider...

Dropping the center wheel 1/8" - 3/18" works very well. However, there may be designs that are more efficient if all 3 wheels on a side are at the same height (same bearing plate is being used, etc.). If this is the situation, instead of dropping the center wheel, you can make the center wheel have a slightly larger diameter and still achieve this needed "rock" dynamic that enables a robot to turn on the center pivot.

In order to do this, you can make your center wheel have a slightly thicker tread... or make your outer wheels have slightly thinner tread thicknesses.

Have fun,
Andy B.