185/75 R15 doesn't belong to the most popular dimensions for summer 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 (185mm), which means the sidewall height has 138.75 mm. The wheel diameter is R15, which means it fits to a 15 inch/381mm diameter wheel. The total circumference of the tyre is 2068.74 mm, which is very similar to 295/30 R19(2072.19 mm), 225/45 R18(2072.51 mm), 205/55 R17(2064.97 mm), 195/65 R16(2073.14 mm), 225/50 R17(2063.4 mm), 285/35 R18(2063.08 mm), 215/65 R15(2075.02 mm).