235/55 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 - 55 is height of the tyre, which is calculated as 55% of the tyre width (235mm), which means the sidewall height has 129.25 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 265/65 R17(2438.82 mm), 205/55 R15(1905.38 mm), 275/30 R21(2194.09 mm), 205/70 R15(2098.58 mm), 275/40 R21(2366.88 mm), 215/45 R17(1964.44 mm), 275/55 R19(2466.46 mm). You can find 235/55 R18 on 20 car models - mainly Audi, Lexus, SsangYong, Volvo, Cadillac.