Falken Azenis FK510 is a summer tyre made in total of 113 sizes, ranging from R17 to R17 - this particular dimension is R20, which means it fits to a 20 inch/508mm diameter wheel. 305/25 R20 is 100mm wider than the narrowest dimension (205) and -70mm narrower than the widest one (235). This tyre profile of 25 means the sidewall height of the tyre is 25% of the tyre width (305mm), which results in 76.25mm sidewall height. In 305/25 R20, there is only one possible speed index for Falken Azenis FK510 - "Y", which is good for speeds up to 300 km/h.