Pirelli P ZERO PZ4 is a summer tyre made in total of 310 sizes, ranging from R17 to R17 - this particular dimension is R21, which means it fits to a 21 inch/533.4mm diameter wheel. 325/30 R21 is 100mm wider than the narrowest dimension (225) and 10mm narrower than the widest one (335). 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 Pirelli P ZERO PZ4 - "Y", which is good for speeds up to 300 km/h. In 325/30 R21, P ZERO PZ4 usually competes against P ZERO, which is a tyre from Pirelli with a rating of 88%, compared to 89% of the Pirelli in question.