255/70 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 - 70 is height of the tyre, which is calculated as 70% of the tyre width (255mm), which means the sidewall height has 178.5 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 255/45 R20(2316.92 mm), 185/75 R16(2148.54 mm), 255/65 R16(2318.18 mm), 195/50 R16(1889.35 mm), 265/35 R18(2019.1 mm), 195/65 R15(1993.34 mm), 265/40 R21(2341.74 mm).