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 205/60 R16(2049.58 mm), 275/40 R18(2127.49 mm), 215/40 R17(1896.89 mm), 275/45 R21(2453.27 mm), 215/55 R17(2099.53 mm), 285/30 R19(2053.34 mm), 215/70 R16(2222.36 mm).