235/40 R17 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 (235mm), which means the sidewall height has 94 mm. The wheel diameter is R17, which means it fits to a 17 inch/431.8mm diameter wheel. The total circumference of the tyre is mm, which is very similar to 275/45 R19(2293.68 mm), 215/50 R18(2111.78 mm), 275/70 R16(2486.26 mm), 215/65 R17(2234.61 mm), 285/35 R21(2302.47 mm), 225/35 R19(2010.93 mm), 285/50 R20(2491.28 mm).