The2nd number 45 is used to calculate the sidewall height or "aspect ratio", by percentage. So, the sidewall height of a 225/45 R 18 tire is 60% of 225 = 192. The 3rd number 18 Given77% while driving a BMW 325 coupe (235/40 R18) on a combination of roads for 3,500 spirited miles Good handling in wet and dry conditions, comfortable as well however not as durable as i expected. (235/45 R18) on mostly motorways for 14,000 average miles Had these for approx 14K miles having done one swap front-rear to Thefirst number 235 is the tire width in millimeters. The 2nd number 40 is used to calculate the sidewall height or "aspect ratio", by percentage. So, the sidewall height of a 235/40 R 18 tire is 60% of 235 = 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 Ifyou are going from 225/40/18 to 235/40/18 dont worry about it you wont notice the difference. I recently switched from stock 17" Type 44's with 235/45's to staggered 18's with 235/40's front and 265/35's rear. The car's handling has improved markedly (although I also went with a better tire, so that gets some credit as well). Albota- 30 decembrie 2023. Set de 6 cauciucuri Continental 235/45/R18. 700 lei Prețul e negociabil. Second Hand. Bucuresti, Sectorul 3 - 04 decembrie 2023. Anvelope / Cauciucuri Vara Pirelli Cinturato P7 235 45 R18 DOT2318. 130 lei Prețul e negociabil. Second Hand. Sibiu - 15 decembrie 2023. 23550-R18 tires are 1.85 inches (47 mm) larger in diameter than 235/40-R18 tires and the speedometer difference is 6.8%. Inthe tire comparison table above, you can see a detailed calculation of the size difference between 235/60 R18 and 245/45 R20 tire. The calculation results are presented in the form of visual infographics, on which tire with size 235/60 R18 is on top, and tire with size 245/45 R20 below. Both in the table and in the graph, the tires are wpHF0.