Changing to smaller wheels for better ride - Mercedes B180d?

[rjfp1962]

A friend of mine owns a Mercedes-Benz b180 AMG Line Executive (2016) running on 18" wheels with 225/40 18 tyres. He'd like to make the ride more comfortable by possibly going down to 16" wheels with 205/55 16 tyres? I'm not sure about clearances regarding the brake discs and callipers, and would welcome any advise or other options anyone has?

Thanks in advance...