here this will help you
215 = the width of the tire in millimeters, from sidewall edge to sidewall edge.
45 or 40 = the ratio of the sidewall height to the total width of the tire as a percentage. If this is missing, it is assumed to be 82%. If the number is larger than 200, then this is the diameter of the entire tire in millimeters.
17 = diameter of the rim
