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 255/45 R20(2316.92 mm), 185/75 R14(1988.94 mm), 255/65 R16(2318.18 mm), 195/50 R15(1809.56 mm), 265/30 R22(2255.04 mm), 195/65 R14(1913.54 mm), 265/40 R20(2261.95 mm).