Heya FlaAveo5 - there is no such thing as a stupid question, moving on, are you baiting me? On the R14 compatible rim there are 55, 60, 65, 70, and 75 size tires available. It depends on what you are looking for. If you like to rev your motor and want more torque the 55 series is what you want. If you want to 'raise your car' because it is winter and you don't want it to be a 'snow-plow' you would choose 75 series tires.
The best way I answer this question is to refer to the miata tire calculator. I think 3rd party links are allowed so here goes again:
Here it is.