185/70 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 (185mm), which means the sidewall height has 129.5 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 235/35 R20(2112.72 mm), 235/50 R17(2094.81 mm), 235/60 R17(2242.47 mm), 155/65 R13(1670.38 mm), 245/30 R20(2057.74 mm), 160/60 R18(2039.52 mm), 245/40 R20(2211.68 mm).