Continental Wintercontact Ts870P is a tyre made in total of 60 sizes, ranging from R16 to R16 - this particular dimension is R21, which means it fits to a 21 inch/533.4mm diameter wheel. 315/40 R21 is 100mm wider than the narrowest dimension (215) and -20mm narrower than the widest one (295). This tyre profile of 40 means the sidewall height of the tyre is 40% of the tyre width (315mm), which results in 126mm sidewall height. In 315/40 R21, there is only one possible speed index for Continental Wintercontact Ts870P - "V", which is good for speeds up to 240 km/h.