Hankook Winter I-Cept iOn X is a winter tyre made in total of 23 sizes, ranging from R18 to R18 - this particular dimension is R21, which means it fits to a 21 inch/533.4mm diameter wheel. This tyre profile of 45 means the sidewall height of the tyre is 45% of the tyre width (235mm), which results in 105.75mm sidewall height. In 235/45 R21, there is only one possible speed index for Hankook Winter I-Cept iOn X - "V", which is good for speeds up to 240 km/h.