205/55 R15 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 (205mm), which means the sidewall height has 112.75 mm. The wheel diameter is R15, which means it fits to a 15 inch/381mm diameter wheel. The total circumference of the tyre is mm, which is very similar to 175/65 R13(1752.07 mm), 255/30 R20(2076.59 mm), 180/60 R17(2035.12 mm), 255/40 R21(2316.61 mm), 185/60 R16(1974.18 mm), 255/55 R19(2397.35 mm), 190/55 R17(2013.13 mm).