195/45 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 - 45 is height of the tyre, which is calculated as 45% of the tyre width (195mm), which means the sidewall height has 87.75 mm. The wheel diameter is R15, which means it fits to a 15 inch/381mm diameter wheel. The total circumference of the tyre is mm, which is very similar to 205/40 R17(1871.76 mm), 265/65 R17(2438.82 mm), 205/55 R16(1985.17 mm), 275/30 R21(2194.09 mm), 205/75 R16(2242.78 mm), 275/40 R21(2366.88 mm), 215/45 R18(2044.23 mm).