225/35 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 - 35 is height of the tyre, which is calculated as 35% of the tyre width (225mm), which means the sidewall height has 78.75 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 165/60 R15(1818.98 mm), 245/45 R19(2208.85 mm), 170/80 R15(2051.46 mm), 245/70 R16(2354.31 mm), 175/70 R14(1886.84 mm), 255/40 R17(1997.42 mm), 185/55 R15(1836.26 mm).