325/30 R21 doesn't belong to the most popular dimensions for all-tests tyres - there are tyre models available, which can be compared to
325/25 R20,
155/60 R15,
155/65 R13. Let's break down the sizing - 30 is height of the tyre, which is calculated as 30% of the tyre width (325mm), which means the sidewall height has 97.5 mm. The wheel diameter is R21, which means it fits to a 21 inch/533.4mm diameter wheel. The total circumference of the tyre is mm, which is very similar to 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), 255/55 R19
(2397.35 mm), 195/40 R17
(1846.63 mm).
