Better Fuel Economy Factory Ratios Increased Power. vs 235/50-18 vs 275/40-18. 245/60-R18 tires are 2.89 inches (73.5 mm) larger in diameter than 245/45-R18 tires and the speedometer difference is 9.8%. 5861. Better Fuel Economy Factory Ratios Increased Power. 245/40-R19 tires are 2.89 inches (73.5 mm) smaller in diameter than 245/55-R19 tires and the speedometer difference is 9.7%. In the tire comparison table above, you can see a detailed calculation of the size difference between 245/45 R18 and 245/50 R18 tire. The calculation results are presented in the form of visual infographics, on which tire with size 245/45 R18 is on top, and tire with size 245/50 R18 below. Both in the table and in the graph, the tires are Also, the online application calculates the difference in real speed and speedometer readings if the difference between tire 245/45 R20 and tire 245/50 R20 is significant. Calculate the difference in inches. If you want to compare other tire sizes, then select their sizes in the drop-down fields and click on the green button. In the tire comparison table above, you can see a detailed calculation of the size difference between 225/50 R17 and 245/40 R18 tire. The calculation results are presented in the form of visual infographics, on which tire with size 225/50 R17 is on top, and tire with size 245/40 R18 below. Both in the table and in the graph, the tires are fROi.