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 205/45 R16(1856.37 mm), 265/70 R16(2442.27 mm), 205/55 R19(2224.56 mm), 275/35 R20(2200.69 mm), 215/35 R18(1909.15 mm), 275/45 R19(2293.68 mm), 215/50 R18(2111.78 mm).