Avon ZV7 is a summer tyre made in total of 58 sizes, ranging from R15 to R15 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 235/55 R18 is 50mm wider than the narrowest dimension (185) and 20mm narrower than the widest one (255). This tyre profile of 55 means the sidewall height of the tyre is 55% of the tyre width (235mm), which results in 129.25mm sidewall height. In 235/55 R18, ZV7 usually competes against Road Performance, which is a tyre from Riken with a rating of 1%, compared to 24% of the Avon in question.