225/55 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 (225mm), which means the sidewall height has 123.75 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 275/65 R17(2479.66 mm), 215/65 R15(2075.02 mm), 285/35 R19(2142.88 mm), 215/85 R16(2425 mm), 285/45 R20(2401.75 mm), 225/45 R19(2152.31 mm), 295/30 R20(2151.99 mm). You can find 225/55 R18 on 24 car models - mainly Peugeot, CITROËN, Jeep, Mitsubishi, Audi.