Most mirror extensions vibrate badly and are useless. I've seen ones that slip-on over the existing mirrors and extend outward. These seem like a good solution but I don't know if they make them for X5's. Sorry.

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Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual