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 235/45 R18(2100.78 mm), 235/55 R19(2328.23 mm), 235/70 R16(2310.33 mm), 160/60 R14(1720.34 mm), 245/40 R17(1972.29 mm), 165/65 R14(1791.02 mm), 245/45 R20(2288.65 mm).