145/70 R12 doesn't belong to the most popular dimensions for winter 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 (145mm), which means the sidewall height has 101.5 mm. The wheel diameter is R12, which means it fits to a 12 inch/304.8mm diameter wheel. The total circumference of the tyre is mm, which is very similar to 195/70 R16(2134.4 mm), 265/45 R21(2425 mm), 205/45 R17(1936.16 mm), 265/70 R16(2442.27 mm), 205/60 R15(1969.78 mm), 275/35 R20(2200.69 mm), 215/40 R16(1817.1 mm). There are multiple speed indexes available for winter tyres in 145/70 R12: Q(160km/h), T(190km/h). The same goes for weight indexes: 69.