Importing Tire Model

I am having trouble importing only a tire model. I see how to access a full vehicle assembly through Assembly Wizard but I would like to know where those model are coming from and if I can use one of the individual models. Is this something that is possible?

Also I have tried making my own tire model by using the Grasub method but I do not know what to do once I have created the template with the script inside.

Any help would be very appreciated. Thank you.