These summer tyre have a diameter of 17". The maximum allowed speed is W (270 km/h), and is the maximum speed the tire may be exposed to.
From Protyre
180/55ZR17 (73W) Pirelli Diablo Rosso IV 180/55R17 (73W) | Protyre
Tirendo
Pirelli Diablo Rosso IV Corsa ( 180/55 ZR17 TL (73W) Rear wheel, M/C )