1 I am looking to decide between these 2 tire sizes for an 18x8.5 wheel. I drive an EX-T with factory 17" wheels and I know the Si has the 235 keep 24550-R18 tires are 1.46 inches (37 mm) smaller in diameter than 235/60-R18 tires and the speedometer difference is 5.0%. Thecalculation results are presented in the form of visual infographics, on which tire with size 235/50 R18 is on top, and tire with size 225/50 R18 below. Both in the table and in the graph, the tires are compared according to the following indicators: overall diameter, section width, circumference, sidewall height and clearance. Thedifference in sizes and parameters between the 275/40 R18 tire and 255/40 R18 tire. Detailed calculations and graphics. Calculate the difference in inches. Tire calculator online . Top comparisons; 225/45 R18: 245/40 R18: 245/45 R18: 235/45 R18: 225/50 R17: 22545-18 235/40-18 Difference; Diameter inches (mm) 25.97 (659.7) 25.4 25545-R20 tires are 0.07 inches (1.7 mm) smaller in diameter than 235/60-R18 tires and the speedometer difference is 0.3%. Tiresize comparison 225/45 R18 vs 235/40 R18 Calculate CM INCHES If your speedometer reads: Real speed is: Size difference between 225/45 R18 and 235/40 R18 tires. In the Tiresize comparison 235/40 R18 vs 225/45 R18 Calculate CM INCHES If your speedometer reads: Real speed is: Size difference between 235/40 R18 and 225/45 R18 tires. In the tire comparison table above, you can gdff8U.