Dunlop SP Sport MAXX is a summer tyre made in total of 52 sizes, ranging from R16 to R16 - this particular dimension is R21, which means it fits to a 21 inch/533.4mm diameter wheel. 325/30 R21 is 110mm wider than the narrowest dimension (215) and -20mm narrower than the widest one (305). This tyre profile of 30 means the sidewall height of the tyre is 30% of the tyre width (325mm), which results in 97.5mm sidewall height. In 325/30 R21, there is only one possible speed index for Dunlop SP Sport MAXX - "Y", which is good for speeds up to 300 km/h.