195/55 R20 doesn't belong to the most popular dimensions for tyres - there are tyre models available, which can be compared to 325/30 R21, 155/60 R15, 155/65 R13. Let's break down the sizing - 55 is height of the tyre, which is calculated as 55% of the tyre width (195mm), which means the sidewall height has 107.25 mm. The wheel diameter is R20, which means it fits to a 20 inch/508mm diameter wheel. The total circumference of the tyre is mm, which is very similar to 235/55 R17(2168.64 mm), 235/65 R17(2316.3 mm), 155/70 R13(1719.08 mm), 245/35 R20(2134.71 mm), 165/60 R14(1739.19 mm), 245/45 R18(2129.06 mm), 170/60 R17(1997.42 mm).