245/50 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 (245mm), which means the sidewall height has 122.5 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 205/65 R15(2034.18 mm), 275/40 R19(2207.28 mm), 215/40 R18(1976.69 mm), 275/50 R20(2459.87 mm), 215/55 R18(2179.32 mm), 285/30 R20(2133.14 mm), 215/75 R15(2210.11 mm).