215/45 R18 doesn't belong to the most popular dimensions for summer tyres - there are 16 tyre models available, which can be compared to 195/50 R15, 165/65 R14, 190/55 R17. Let's break down the sizing - 45 is height of the tyre, which is calculated as 45% of the tyre width (215mm), which means the sidewall height has 96.75 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 2044.23 mm, which is very similar to 285/25 R20(2043.61 mm), 225/60 R15(2045.18 mm), 185/80 R14(2047.06 mm), 275/35 R18(2041.09 mm), 200/55 R17(2047.69 mm), 160/60 R18(2039.52 mm), 245/45 R17(2049.26 mm). There are multiple speed indexes available for summer tyres in 215/45 R18: T(190km/h), V(240km/h), W(270km/h), Y(300km/h). The same goes for weight indexes: 83, 89, 93.