Assuming this is a contour derived from a spline curve, you should be able to apply a tangency constraint between the wheel and the surface, and have the wheel follow the surface. Dunno about a very complex spline, I've only ever done this with "simple" splines that aren't very far off from ellipses.
If the contour is composed of many seperate geometric entitites, you may need to look at each entity seperately, i.e. you could only constrain the wheel to be tangent to one entity's surface at a time.
Along with what btrueblood said, you could create a spline surface on the contour that you want to follow. This would give you the smooth entity you need and you could then make it invisible when you are done constraining.
Is there any way to get it to run from one surface to another. For instance from a curved surface to a straight surface that were not drawn as one face.
If you have Inventor Professional with Dynamic Simulation there are more options. Otherwise Transistional constraint. Zip and attach what you have so far if you can't figure it out.
