Michelin e.Primacy is a summer tyre made in total of 107 sizes, ranging from R15 to R15 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 245/50 R18 is 80mm wider than the narrowest dimension (165) and -20mm narrower than the widest one (225). This tyre profile of 50 means the sidewall height of the tyre is 50% of the tyre width (245mm), which results in 122.5mm sidewall height. In 245/50 R18, there is only one possible speed index for Michelin e.Primacy - "H", which is good for speeds up to 210 km/h.