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 225/45 R19(2152.31 mm), 295/30 R20(2151.99 mm), 225/60 R15(2045.18 mm), 305/25 R20(2075.02 mm), 225/75 R16(2337.03 mm), 235/45 R18(2100.78 mm), 235/55 R19(2328.23 mm).