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 235/45 R19
(2180.58 mm), 235/55 R20
(2408.03 mm), 235/75 R15
(2304.36 mm), 160/60 R15
(1800.13 mm), 245/40 R18
(2052.09 mm), 165/65 R15
(1870.82 mm), 245/50 R18
(2206.03 mm).
