285/30 R21 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 - 30 is height of the tyre, which is calculated as 30% of the tyre width (285mm), which means the sidewall height has 85.5 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 175/80 R14
(1996.8 mm), 255/40 R18
(2077.22 mm), 185/60 R14
(1814.58 mm), 255/50 R19
(2317.24 mm), 185/80 R14
(2047.06 mm), 255/65 R17
(2397.98 mm), 195/55 R15
(1870.82 mm).
