Continental CrossContact RX is a summer tyre made in total of 36 sizes, ranging from R16 to R16 - this particular dimension is R21, which means it fits to a 21 inch/533.4mm diameter wheel. This tyre profile of 40 means the sidewall height of the tyre is 40% of the tyre width (255mm), which results in 102mm sidewall height. In 255/40 R21, there are 2 possible speed indexes for Continental CrossContact RX - "V","W", which are good for speeds up to 240, 270 km/h.