285/35 R21 doesn't belong to the most popular dimensions for winter tyres - there are 3 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 (285mm), which means the sidewall height has 99.75 mm. The wheel diameter is R21, which means it fits to a 21 inch/533.4mm diameter wheel. The total circumference of the tyre is 2302.47 mm, which is very similar to 235/75 R15(2304.36 mm), 275/55 R17(2306.87 mm), 205/80 R16(2307.19 mm), 235/70 R16(2310.33 mm), 275/45 R19(2293.68 mm), 225/55 R19(2293.68 mm), 295/30 R22(2311.58 mm). There are multiple speed indexes available for winter tyres in 285/35 R21: H(210km/h), V(240km/h), W(270km/h). The same goes for weight indexes: 105, 108.