Nokian WR A4 is a winter tyre made in total of 59 sizes, ranging from R16 to R16 - this particular dimension is R18, which means it fits to a 18 inch/457.2mm diameter wheel. 225/45 R18 is 20mm wider than the narrowest dimension (205) and 20mm narrower than the widest one (245). This tyre profile of 45 means the sidewall height of the tyre is 45% of the tyre width (225mm), which results in 101.25mm sidewall height. In 225/45 R18, there is only one possible speed index for Nokian WR A4 - "V", which is good for speeds up to 240 km/h. In 225/45 R18, WR A4 usually competes against ContiWinterContact TS 850P, which is a tyre from Continental with a rating of 53%, compared to 0% of the Nokian in question. Latest test in 225/45 R18 was held by AutoMotorSport in 2017, where WR A4 received rating "Still recommended" and finished on the 7. place. It was tested on a BMW 4.
