I have a Make_Model table which list make and models. Example:
Make Model
Honda Civic
Honda Fit
Nissan Maxima
Nissan Tiida
I have created a Cars table which used both fields in the make and model table as reference. So if the user when creating a new car select Honda, the value to choose from in the Model field is Civic and Fit and if they select Nissan values available would be Maxima and Tiida.