Toyo Proxes Sport Suv is a tyre made in total of 20 sizes, ranging from R17 to R17 - 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 Toyo Proxes Sport Suv - "Y", which is good for speeds up to 300 km/h.