Michelin Pilot Sport EV is a summer tyre made in total of 50 sizes, ranging from R19 to R19 - this particular dimension is R21, which means it fits to a 21 inch/533.4mm diameter wheel. 305/30 R21 is 70mm wider than the narrowest dimension (235) and -30mm narrower than the widest one (275). This tyre profile of 30 means the sidewall height of the tyre is 30% of the tyre width (305mm), which results in 91.5mm sidewall height. In 305/30 R21, there is only one possible speed index for Michelin Pilot Sport EV - "Y", which is good for speeds up to 300 km/h.