Goodyear Eagle F1 Asymmetric 6 is a summer tyre made in total of 197 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 110mm wider than the narrowest dimension (205) and 10mm narrower than the widest one (325). 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 Goodyear Eagle F1 Asymmetric 6 - "Y", which is good for speeds up to 300 km/h.