265/50 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 - 50 is height of the tyre, which is calculated as 50% of the tyre width (265mm), which means the sidewall height has 132.5 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 R20
(2095.44 mm), 195/60 R16
(2011.88 mm), 265/40 R18
(2102.35 mm), 195/80 R15
(2177.12 mm), 265/55 R19
(2431.91 mm), 205/50 R16
(1920.77 mm).