235/45 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 - 45 is height of the tyre, which is calculated as 45% of the tyre width (235mm), which means the sidewall height has 105.75 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 165/60 R14
(1739.19 mm), 245/45 R17
(2049.26 mm), 170/60 R17
(1997.42 mm), 245/60 R18
(2359.96 mm), 175/70 R13
(1807.04 mm), 255/35 R19
(2076.91 mm), 185/55 R14
(1756.46 mm).
