255/40 R21 - Best tyres 2025 - market overview, tests, reviews

255/40 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 (255mm), which means the sidewall height has 102 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 235/60 R18(2322.27 mm), 155/65 R14(1750.18 mm), 245/35 R18(1975.12 mm), 160/70 R17(2060.26 mm), 245/40 R21(2291.48 mm), 165/80 R13(1866.73 mm), 245/55 R17(2203.2 mm).