This calculator tells you what tyre sizes to go for based on the size of your rim/mag. For .eg. it gives an answer to the question: « I have 15X 6,5 rims. What's the best tyre size?"
Also, it shows tyre width range for the selected rim: minimum, ideal and maximum tyre widths.
Select your rim size and click on the button "Find Tyre Size". The calculator will then tell you what tyre sizes to go for based for the size of your rim.