Nokian zLine is a summer tyre made in total of 45 sizes, ranging from R16 to R16 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 235/40 R18 is 30mm wider than the narrowest dimension (205) and 10mm narrower than the widest one (245). This tyre profile of 40 means the sidewall height of the tyre is 40% of the tyre width (235mm), which results in 94mm sidewall height. In 235/40 R18, there is only one possible speed index for Nokian zLine - "Y", which is good for speeds up to 300 km/h. In 235/40 R18, zLine usually competes against Powerproof, which is a tyre from Nokian with a rating of 76%, compared to 42% of the Nokian in question.