Continental CrossContact UHP is a summer tyre made in total of 47 sizes, ranging from R16 to R16 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 255/55 R18 is 20mm wider than the narrowest dimension (235) and 50mm narrower than the widest one (305). This tyre profile of 55 means the sidewall height of the tyre is 55% of the tyre width (255mm), which results in 140.25mm sidewall height. In 255/55 R18, there are 3 possible speed indexes for Continental CrossContact UHP - "W","Y","V", which are good for speeds up to 270, 300, 240 km/h.