235/45 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 - 45 is height of the tyre, which is calculated as 45% of the tyre width (235mm), which means the sidewall height has 105.75 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 195/45 R16(1828.09 mm), 265/30 R21(2175.24 mm), 195/60 R16(2011.88 mm), 265/40 R19(2182.15 mm), 195/80 R15(2177.12 mm), 265/55 R19(2431.91 mm), 205/50 R16(1920.77 mm).