Pirelli P ZERO Corsa is a summer tyre made in total of 36 sizes, ranging from R19 to R19 - this particular dimension is R21, which means it fits to a 21 inch/533.4mm diameter wheel. 355/25 R21 is 130mm wider than the narrowest dimension (225) and -30mm narrower than the widest one (325). This tyre profile of 25 means the sidewall height of the tyre is 25% of the tyre width (355mm), which results in 88.75mm sidewall height. In 355/25 R21, there is only one possible speed index for Pirelli P ZERO Corsa - "Y", which is good for speeds up to 300 km/h.