275/60 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 - 60 is height of the tyre, which is calculated as 60% of the tyre width (275mm), which means the sidewall height has 165 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 185/60 R16(1974.18 mm), 255/55 R18(2317.55 mm), 190/55 R17(2013.13 mm), 255/70 R16(2398.29 mm), 195/55 R20(2269.8 mm), 265/35 R20(2178.69 mm), 195/70 R15(2054.6 mm).