175/50 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 - 50 is height of the tyre, which is calculated as 50% of the tyre width (175mm), which means the sidewall height has 87.5 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 165/70 R14(1842.86 mm), 245/50 R20(2365.62 mm), 175/65 R14(1831.86 mm), 255/30 R20(2076.59 mm), 180/65 R16(2011.88 mm), 255/40 R21(2316.61 mm), 185/65 R14(1872.7 mm).