235/55 R20 doesn't belong to the most popular dimensions for allround tyres - there are 1 tyre models available, which can be compared to 155/60 R15, 170/60 R17, 160/60 R14. Let's break down the sizing - 55 is height of the tyre, which is calculated as 55% of the tyre width (235mm), which means the sidewall height has 129.25 mm. The wheel diameter is R20, which means it fits to a 20 inch/508mm diameter wheel. The total circumference of the tyre is 2408.03 mm, which is very similar to 285/45 R20(2401.75 mm), 295/40 R21(2417.14 mm), 255/70 R16(2398.29 mm), 255/65 R17(2397.98 mm), 255/60 R18(2397.66 mm), 255/55 R19(2397.35 mm), 255/50 R20(2397.04 mm). There are multiple speed indexes available for allround tyres in 235/55 R20: V(240km/h). The same goes for weight indexes: 102.