205/35 R18 doesn't belong to the most popular dimensions for summer tyres - there are 2 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 (205mm), which means the sidewall height has 71.75 mm. The wheel diameter is R18, which means it fits to a 18 inch/457.2mm diameter wheel. The total circumference of the tyre is 1887.15 mm, which is very similar to 175/70 R14(1886.84 mm), 195/50 R16(1889.35 mm), 215/45 R16(1884.64 mm), 185/60 R15(1894.38 mm), 215/40 R17(1896.89 mm), 185/65 R14(1872.7 mm), 205/40 R17(1871.76 mm). There are multiple speed indexes available for summer tyres in 205/35 R18: Y(300km/h). The same goes for weight indexes: 81.