Bridgestone Potenza Sport is a summer tyre made in total of 117 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 120mm wider than the narrowest dimension (205) and -40mm narrower than the widest one (285). 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 Bridgestone Potenza Sport - "Y", which is good for speeds up to 300 km/h. In 325/30 R21, Potenza Sport usually competes against Pilot Sport 4, which is a tyre from Michelin with a rating of 94%, compared to 93% of the Bridgestone in question.