Nokian Hakkapeliitta R3 is a winter tyre made in total of 79 sizes, ranging from R14 to R14 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 225/45 R18 is 50mm wider than the narrowest dimension (175) and 40mm narrower than the widest one (265). This tyre profile of 45 means the sidewall height of the tyre is 45% of the tyre width (225mm), which results in 101.25mm sidewall height. In 225/45 R18, there is only one possible speed index for Nokian Hakkapeliitta R3 - "T", which is good for speeds up to 190 km/h.