it will fit, tirerack has it listed for the 2006 e90 in 20"
check out this link and you'll see it:
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<a href="http://www.tkqlhce.com/click-1852000-10399928" rel="" target="_top" >TIRERACK</a><img src="http://www.afcyhf.com/image-1852000-10399928" width="1" height="1" border="0">