Nankang SP-9 Cross Sport 315/40 R21

Nankang SP-9 Cross Sport is a tyre made in total of 28 sizes, ranging from R15 to R15 - this particular dimension is R21, which means it fits to a 21 inch/533.4mm diameter wheel. 315/40 R21 is 100mm wider than the narrowest dimension (215) and 0mm narrower than the widest one (315). This tyre profile of 40 means the sidewall height of the tyre is 40% of the tyre width (315mm), which results in 126mm sidewall height.