BuddyPress.org

I m working on a site and in the profile component after the base group “Name” I would like to add another Field Group like say “Cars”. I am able to do that but what I am stuck with, that I would like the users to be to use the option of selecting lets say “Make of Vehicle” from a drop down menu and next to it would be a drop down menu “Model of Vehicle” which would load depending on the make of vehicle selected by the user. For example if the user selects “Make of vehicle” as Honda, then the Make of vehicle drop down menu now allows user to select from “corolla, yaris, 4runner, camry”.
Could any one help me with this, I believe I need to edit the bp-xprofile.php file but dont know what part.