Inthis case, the 235/40r18 tire has an aspect ratio of 40%, while the 235/45r18 tire has an aspect ratio of 45%. This means the 235/45r18 tire has a taller sidewall than the 235/40r18 tire. 235/45r18 vs 235/40r18 This table provides a quick overview of the main differences between the two sizes. Fitment Guide. The 235/45R18 is 3.6% larger in Sizedifference between 275/40 R18 and 255/55 R18 tires. In the tire comparison table above, you can see a detailed calculation of the size difference between 275/40 R18 and 255/55 R18 tire. The calculation results are presented in the form of visual infographics, on which tire with size 275/40 R18 is on top, and tire with size 255/55 R18 below. Thedifference in sizes and parameters between the 245/40 R18 tire and 225/45 R18 tire. Detailed calculations and graphics. Thedifference in sizes and parameters between the 245/60 R18 tire and 245/45 R20 tire. Detailed calculations and graphics. Calculate the difference in inches. Tire calculator online . Top comparisons; 235/55 R18: 275/40 R20: 245/40 R20: 255/40 R20: 225/65 R17: The245 40r18 has a diameter of 25.72 inches, while the 225 40r18 has a diameter of 25.09 inches. This means that the 245 40r18 is slightly larger than the 225 40r18. The larger 6089 Better Fuel Economy Factory Ratios Increased Power. 245/40-R18 tires are 0.04 inches (0.9 mm) smaller in diameter than 245/35-R19 tires and the speedometer difference is 0.2%. The2nd number 50 is used to calculate the sidewall height or "aspect ratio", by percentage. So, the sidewall height of a 245/50 R 20 tire is 60% of 245 = 192. The 3rd number 20 (generally preceded by an "R") is Rim Diameter in inches. This is the diameter of the rims bead seat base, not the diameter of the outer rim edge. Inthe tire comparison table above, you can see a detailed calculation of the size difference between 215/45 R18 and 225/40 R18 tire. The calculation results are presented in the form of visual infographics, on which tire with 27540-R18 tires are 0.02 inches (0.5 mm) smaller in diameter than 245/45-R18 tires and the speedometer difference is 0.1%. 23540-R19 tires are 0.28 inches (7.1 mm) smaller in diameter than 245/45-R18 tires and the speedometer difference is 1.1% 99kgo.