Michelin Primacy 4 is a summer tyre made in total of 240 sizes, ranging from R15 to R15 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 245/45 R18 is 80mm wider than the narrowest dimension (165) and 10mm narrower than the widest one (255). 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 are 2 possible speed indexes for Michelin Primacy 4 - "W","Y", which are good for speeds up to 270, 300 km/h. In 245/45 R18, Primacy 4 usually competes against PremiumContact 6, which is a tyre from Continental with a rating of 87%, compared to 89% of the Michelin in question.