Imperial All Season Driver is a allround tyre made in total of 133 sizes, ranging from R13 to R13 - this particular dimension is R20, which means it fits to a 20 inch/508mm diameter wheel. 235/50 R20 is 90mm wider than the narrowest dimension (145) and 40mm narrower than the widest one (275). This tyre profile of 50 means the sidewall height of the tyre is 50% of the tyre width (235mm), which results in 117.5mm sidewall height. In 235/50 R20, there is only one possible speed index for Imperial All Season Driver - "W", which is good for speeds up to 270 km/h.