coordinate system
 

I'm doing a car external aerodinamic analysis, the model at the moment is very simple and I have to consider rotating wheel.The wheel are modeled with simple surface and I'd like to consider them like rotating walls and assign an appropriate angular velocity. So I have to create a cylindrical coordinate system with the z axes coinciding with the wheel rotation axes and assign an angular velocity. How can create the coordinate system exactly in the center of the wheel???? thanks a lot