325/40 R21 - Best tyres 2025 - market overview, tests, reviews

325/40 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 - 40 is height of the tyre, which is calculated as 40% of the tyre width (325mm), which means the sidewall height has 130 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 165/80 R13(1866.73 mm), 245/55 R17(2203.2 mm), 175/65 R15(1911.66 mm), 255/35 R18(1997.11 mm), 185/50 R16(1857.94 mm), 255/45 R17(2077.54 mm), 185/65 R15(1952.5 mm).