Yokohama Bluearth AE-50 is a summer tyre made in total of 12 sizes, ranging from R14 to R14 - 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 -10mm narrower than the widest one (235). 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 Yokohama Bluearth AE-50 - "W", which is good for speeds up to 270 km/h.