In the e90post detailing forum one of the stickies mentions how to wash the car in the winter... guy recommends a touchless auto wash for several reasons.
I agree about the rails, though. Scrrrrrrrrrrrrrrrrrrrape.
2015 SO/SO MT M3 :: Exec : Lighting : Adaptive : HK : CF trim : Full leather : DAP : Black 19's : sunshade
Crystalline tint 40%/70% on windshield : M performance mirrors, spoiler, splitters, lip : RKP diffuser : Fully dechromed
Bavsound Stage 1 : V1 Savvy hardwired : Self-coded