Michelin PILOT ALPIN 5 is a winter tyre made in total of 102 sizes, ranging from R16 to R16 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 255/40 R18 is 50mm wider than the narrowest dimension (205) and 30mm narrower than the widest one (285). This tyre profile of 40 means the sidewall height of the tyre is 40% of the tyre width (255mm), which results in 102mm sidewall height. In 255/40 R18, there is only one possible speed index for Michelin PILOT ALPIN 5 - "V", which is good for speeds up to 240 km/h. In 255/40 R18, PILOT ALPIN 5 usually competes against Winter i*cept evo3 W330, which is a tyre from Hankook with a rating of 89%, compared to 98% of the Michelin in question.