235/30 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 - 30 is height of the tyre, which is calculated as 30% of the tyre width (235mm), which means the sidewall height has 70.5 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 200/55 R17
(2047.69 mm), 265/55 R19
(2431.91 mm), 205/50 R17
(2000.57 mm), 275/30 R19
(2034.5 mm), 205/65 R16
(2113.98 mm), 275/40 R19
(2207.28 mm), 215/45 R16
(1884.64 mm).
