255/45 R17 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 - 45 is height of the tyre, which is calculated as 45% of the tyre width (255mm), which means the sidewall height has 114.75 mm. The wheel diameter is R17, which means it fits to a 17 inch/431.8mm diameter wheel. The total circumference of the tyre is mm, which is very similar to 175/65 R13(1752.07 mm), 255/30 R19(1996.8 mm), 180/60 R17(2035.12 mm), 255/40 R20(2236.81 mm), 185/60 R16(1974.18 mm), 255/55 R19(2397.35 mm), 190/55 R17(2013.13 mm).