Which channels can I delete from the cr2?

Each of the wheels is attached to a truck, and each wheel will only ever need to move around its own X axis.  What channels can I safely delete to lighten the cr2?  Last night I cut out everything except the xRot, but that caused the wheels to rotate around the centerpoint of the entire figure. 

Wheels:  only move around their own x axis
Trucks:  Rotate around x y and z axis