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 175/60 R14
(1776.88 mm), 245/70 R17
(2434.11 mm), 175/80 R14
(1996.8 mm), 255/40 R18
(2077.22 mm), 185/60 R14
(1814.58 mm), 255/50 R19
(2317.24 mm), 185/80 R14
(2047.06 mm).