265/30 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 (265mm), which means the sidewall height has 79.5 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 205/40 R18
(1951.56 mm), 265/70 R15
(2362.48 mm), 205/55 R17
(2064.97 mm), 275/35 R19
(2120.89 mm), 205/80 R16
(2307.19 mm), 275/45 R18
(2213.88 mm), 215/50 R17
(2031.98 mm).
