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 235/35 R20(2112.72 mm), 235/50 R17(2094.81 mm), 235/60 R17(2242.47 mm), 155/65 R13(1670.38 mm), 245/30 R20(2057.74 mm), 160/60 R18(2039.52 mm), 245/40 R20(2211.68 mm).