Nokian Rotiiva AT Plus is a summer tyre made in total of 15 sizes, ranging from R16 to R16 - this particular dimension is R20, which means it fits to a 20 inch/508mm diameter wheel. 305/55 R20 is 80mm wider than the narrowest dimension (225) and 0mm narrower than the widest one (305). This tyre profile of 55 means the sidewall height of the tyre is 55% of the tyre width (305mm), which results in 167.75mm sidewall height. In 305/55 R20, there is only one possible speed index for Nokian Rotiiva AT Plus - "S", which is good for speeds up to 180 km/h.