305/40 R20 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 (305mm), which means the sidewall height has 122 mm. The wheel diameter is R20, which means it fits to a 20 inch/508mm diameter wheel. The total circumference of the tyre is mm, which is very similar to 205/80 R16
(2307.19 mm), 275/40 R22
(2446.67 mm), 215/50 R17
(2031.98 mm), 275/65 R17
(2479.66 mm), 215/65 R16
(2154.82 mm), 285/35 R19
(2142.88 mm), 225/35 R18
(1931.14 mm).
