I think that step is to visually mimic the BBS design where they scoop out material in the spokes to make the wheels lighter. The scoop catches light on BBS wheels and these casts (and other) wheels fake that sliver of a highlight with the slim step behind the spokes. IMO.
Price shipped to 32707 for 19" in silver for a LCI e90 please.
My Current: 2010 Sapphire Black Metallic 335i /Sport/DCT/PDC/Nav/Black Leather/CF Wrapped Interior/Gloss Black Grill/More coming...
My Other: 2006 Audi A4/Quartz Grey/Black Leather/E-Codes/APR tune/19" VRM v708s/FK Silverlines/RS4 Front Sway Bar/S4 Mirrors/Black Grill/Arc Audio-Focal Sound system