Michelin Pilot Alpin PA4 is a winter tyre made in total of 115 sizes, ranging from R17 to R17 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 245/45 R18 is 20mm wider than the narrowest dimension (225) and 100mm narrower than the widest one (345). This tyre profile of 45 means the sidewall height of the tyre is 45% of the tyre width (245mm), which results in 110.25mm sidewall height. In 245/45 R18, there is only one possible speed index for Michelin Pilot Alpin PA4 - "V", which is good for speeds up to 240 km/h. In 245/45 R18, Pilot Alpin PA4 usually competes against Blizzak LM-005, which is a tyre from Bridgestone with a rating of 92%, compared to 64% of the Michelin in question.