Pirelli P Zero Winter is a winter tyre made in total of 78 sizes, ranging from R18 to R18 - this particular dimension is R21, which means it fits to a 21 inch/533.4mm diameter wheel. 285/35 R21 is 50mm wider than the narrowest dimension (235) and 10mm narrower than the widest one (295). This tyre profile of 35 means the sidewall height of the tyre is 35% of the tyre width (285mm), which results in 99.75mm sidewall height. In 285/35 R21, there is only one possible speed index for Pirelli P Zero Winter - "H", which is good for speeds up to 210 km/h.