235/40 R20 doesn't belong to the most popular dimensions for allround tyres - there are 0 tyre models available, which can be compared to 155/60 R15, 170/60 R17, 160/60 R14. Let's break down the sizing - 40 is height of the tyre, which is calculated as 40% of the tyre width (235mm), which means the sidewall height has 94 mm. The wheel diameter is R20, which means it fits to a 20 inch/508mm diameter wheel. The total circumference of the tyre is 2186.55 mm, which is very similar to 225/70 R15(2186.55 mm), 265/45 R18(2185.61 mm), 265/40 R19(2182.15 mm), 235/45 R19(2180.58 mm), 215/55 R18(2179.32 mm), 275/30 R21(2194.09 mm), 265/35 R20(2178.69 mm). There are multiple speed indexes available for allround tyres in 235/40 R20: Y(300km/h). The same goes for weight indexes: 96.