trick question!
they're no easier nor harder to keep clean than any other wheels for course
but you could definitely go much longer between washes (on an F90 without CCB brakes) before the wheels start looking like an ashtray no doubt!
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2021 A6 Allroad, 2020 SQ7, 2019 M5 Comp, 2011 GT3
past: A4, S4, X5 4.8is, SLK55, E60 M5, RS4, ML63, E92 M3, Q5, Touareg TDI, Escalade, SQ5, RS7, Velar FE, Q7