305/35 R20 doesn't belong to the most popular dimensions for winter tyres - there are 1 tyre models available, which can be compared to 155/60 R15, 170/60 R17, 160/60 R14. Let's break down the sizing - 35 is height of the tyre, which is calculated as 35% of the tyre width (305mm), which means the sidewall height has 106.75 mm. The wheel diameter is R20, which means it fits to a 20 inch/508mm diameter wheel. The total circumference of the tyre is 2266.66 mm, which is very similar to 225/70 R16(2266.34 mm), 195/55 R20(2269.8 mm), 265/40 R20(2261.95 mm), 235/45 R20(2260.38 mm), 265/35 R21(2258.49 mm), 225/65 R17(2275.46 mm), 215/80 R15(2277.65 mm). There are multiple speed indexes available for winter tyres in 305/35 R20: V(240km/h), W(270km/h). The same goes for weight indexes: 104, 107.