[GregT]

I don't think inventor can do it.

It would be possible to do in solidworks, but would require rediculously complecated equations.

What you're asking inventor to do is change the profile of the tread with respect to the position of a wheel. Unless inventor supports equations or some other way of dynamically changing sketches I'm afraid your out of luck.

You might want to pause and ask yourself why you want to do this. Besides "it will look cool" I can't think of any. Remember that inventor is a CAD program and not ment to handle complex anamation tasks. I agree that it would look cool but your time is probably best spent elsewhere.

Greg