145/70 R12 doesn't belong to the most popular dimensions for summer 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 215/70 R16
(2222.36 mm), 285/35 R22
(2382.27 mm), 225/40 R18
(2001.82 mm), 285/60 R18
(2510.76 mm), 225/55 R16
(2054.29 mm), 295/35 R20
(2244.67 mm), 225/65 R16
(2195.66 mm).
