225/45 R18 doesn't belong to the most popular dimensions for tyres - there are tyre models available, which can be compared to 325/30 R21, 155/60 R15, 155/65 R13. Let's break down the sizing - 45 is height of the tyre, which is calculated as 45% of the tyre width (225mm), which means the sidewall height has 101.25 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 mm, which is very similar to 265/75 R16(2525.53 mm), 205/60 R16(2049.58 mm), 275/40 R18(2127.49 mm), 215/40 R17(1896.89 mm), 275/45 R21(2453.27 mm), 215/55 R17(2099.53 mm), 285/30 R19(2053.34 mm). You can find 225/45 R18 on 35 car models - mainly Mercedes-Benz, BMW, Kia, Subaru, Mazda.