285/50 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 - 50 is height of the tyre, which is calculated as 50% of the tyre width (285mm), which means the sidewall height has 142.5 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 2331.69 mm, which is very similar to 235/55 R19(2328.23 mm), 225/75 R16(2337.03 mm), 295/40 R20(2337.34 mm), 265/35 R22(2338.29 mm), 295/35 R21(2324.46 mm), 235/60 R18(2322.27 mm), 285/45 R19(2321.95 mm). There are multiple speed indexes available for summer tyres in 285/50 R18: W(270km/h). The same goes for weight indexes: 109.