255/75 R17 doesn't belong to the most popular dimensions for allround tyres - there are 0 tyre models available, which can be compared to 155/60 R15, 170/60 R17, 160/60 R14. Let's break down the sizing - 75 is height of the tyre, which is calculated as 75% of the tyre width (255mm), which means the sidewall height has 191.25 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 2558.2 mm, which is very similar to 255/70 R18(2557.88 mm), 275/65 R18(2559.46 mm), 235/85 R16(2531.81 mm), 265/75 R16(2525.53 mm), 265/70 R17(2522.07 mm), 285/65 R17(2520.5 mm), 265/65 R18(2518.61 mm). There are multiple speed indexes available for allround tyres in 255/75 R17: T(190km/h). The same goes for weight indexes: 115.