Please pay attention the size is the full tire diameter not the hub diameter. For example, if tire parameter is 225/75r16, then A=225, B=75, C=16, the calculation formula is: Diameter=A*B/500+C*2.54=225*75/500+16*2.54=74.39cm, 16 inch tire cover will fit it. Replace A B C with your tire data will get corret tire cover size.