Uniroyal RainSport 5 is a summer tyre made in total of 124 sizes, ranging from R15 to R15 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 225/55 R18 is 40mm wider than the narrowest dimension (185) and 70mm narrower than the widest one (295). This tyre profile of 55 means the sidewall height of the tyre is 55% of the tyre width (225mm), which results in 123.75mm sidewall height. In 225/55 R18, there is only one possible speed index for Uniroyal RainSport 5 - "V", which is good for speeds up to 240 km/h.