Bridgestone Alenza 001 is a summer tyre made in total of 57 sizes, ranging from R17 to R17 - this particular dimension is R20, which means it fits to a 20 inch/508mm diameter wheel. 245/45 R20 is 30mm wider than the narrowest dimension (215) and 30mm narrower than the widest one (275). This tyre profile of 45 means the sidewall height of the tyre is 45% of the tyre width (245mm), which results in 110.25mm sidewall height. In 245/45 R20, there is only one possible speed index for Bridgestone Alenza 001 - "W", which is good for speeds up to 270 km/h.
