265/30 R20 doesn't belong to the most popular dimensions for summer tyres - there are 12 tyre models available, which can be compared to 165/60 R15, 185/55 R14, 170/60 R17. Let's break down the sizing - 30 is height of the tyre, which is calculated as 30% of the tyre width (265mm), which means the sidewall height has 79.5 mm. The wheel diameter is R20, which means it fits to a 20 inch/508mm diameter wheel. The total circumference of the tyre is 2095.44 mm, which is very similar to 235/50 R17(2094.81 mm), 205/70 R15(2098.58 mm), 265/35 R19(2098.9 mm), 215/55 R17(2099.53 mm), 305/30 R19(2091.04 mm), 225/35 R20(2090.73 mm), 235/45 R18(2100.78 mm). There are multiple speed indexes available for summer tyres in 265/30 R20: Y(300km/h). The same goes for weight indexes: 94.