245/40 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 - 40 is height of the tyre, which is calculated as 40% of the tyre width (245mm), which means the sidewall height has 98 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 215/75 R15(2210.11 mm), 285/40 R20(2312.21 mm), 225/40 R19(2081.62 mm), 295/25 R20(2059.31 mm), 225/55 R17(2134.08 mm), 295/40 R20(2337.34 mm), 225/65 R17(2275.46 mm). You can find 245/40 R18 on 29 car models - mainly Mercedes-Benz, Audi, Volvo, ALPINA, BMW.