Nokian WR D4 is a winter tyre made in total of 82 sizes, ranging from R13 to R13 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 225/50 R18 is 70mm wider than the narrowest dimension (155) and 50mm narrower than the widest one (275). This tyre profile of 50 means the sidewall height of the tyre is 50% of the tyre width (225mm), which results in 112.5mm sidewall height. In 225/50 R18, there is only one possible speed index for Nokian WR D4 - "H", which is good for speeds up to 210 km/h.
