Bill the drill

Hi everybody , Just joined the forum and was hoping for advice concerning replacing 20 inch sentras with smaller wheels / more rubber . Pot holes have taken their toll and i have had 2 cracked alloys in 2 weeks . I have a 2010 XFS 3.0 litre diesel and on looking around it seems 18 inch wheels are the way forward due to the larger calipers . ( 8.5J x 18 ET49 ? ) Any opinions ? Cheers Bill