Riken Snow is a winter tyre made in total of 55 sizes, ranging from R15 to R15 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 225/40 R18 is 60mm wider than the narrowest dimension (165) and 20mm narrower than the widest one (245). This tyre profile of 40 means the sidewall height of the tyre is 40% of the tyre width (225mm), which results in 90mm sidewall height. In 225/40 R18, there is only one possible speed index for Riken Snow - "V", which is good for speeds up to 240 km/h. In 225/40 R18, Snow usually competes against Winter Sport 5, which is a tyre from Dunlop with a rating of 89%, compared to 7% of the Riken in question.