Here's my blend file

Track.blend

Maybe I'm mistaken, but the file you posted used a "Path" instead of a "Bezier Circle".   You're correct, when I tried moving your rig around, the tracks would fly off the path when moved in one direction. 

I've used a Bezier Circle in my example above.   Rotating / Moving the curve in any direction and the tracks stay on the curve.  Moving the 'track' along the global Z axis is what will make them rotate around the Bezier Circle.  This is what the guy did in the other file. .  He used a Lattice as a handle in order to move the track up and down, there by rotating them around the Curve Circle.

Reddog9
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