225/45-R17 tires are 0.43 inches (10.9 mm) smaller in diameter than 235/40-R18 tires and the speedometer difference is 1.7%. In the tire comparison table above, you can see a detailed calculation of the size difference between 215/45 R18 and 225/45 R18 tire. The calculation results are presented in the form of visual infographics, on which tire with size 215/45 R18 is on top, and tire with size 225/45 R18 below. Both in the table and in the graph, the tires are The first number 225 is the tire width in millimeters. The 2nd number 55 is used to calculate the sidewall height or "aspect ratio", by percentage. So, the sidewall height of a 225/55 R 18 tire is 60% of 225 = 192. The 3rd number 18 (generally preceded by an "R") is Rim Diameter in inches. This is the diameter of the rims bead seat base, not 225/45 r17 225/50 r17 235/40 r18 245/45 r18 215/45 r17 225/45 r18 225/55 r17 245/40 r18 205/40 r17 255/35 r19 235/45 r17 235/55 r17 (1) Based on internal dry circuit lap time tests comparing the MICHELIN ® PILOT ® Sport 4 S (39.25 sec. avg. lap time) versus the Bridgestoneо Potenza S-04 Pole Position (40.70 sec. avg. lap time), Continentalо ExtremeContact TM Sport (40.03 sec. avg. lap time), Pirelliо P ZERO PZ4 (40.24 sec. avg. lap time), and Goodyearо Eagleо F1 225/45-R17. Changes. Dev. 80 mph. Circ. 193.7 cm (6' 4.26") 193.4 cm (6' 4.14") -0.3 cm (-0.12") -0.15% 225: 40: 18: 61.85 (2' 0.35") 194.3 (6' 4.5") 0.3%: 225: .

225 45 r17 vs 225 40 r18