I've driven my X5 on Pismo Beach which is about 4 miles of beach and dunes. There was no problem on the wet or compacted hard sand. I did venture out onto the soft dune sand and as long as I kept moving and stayed on level ground I was OK. I would not trust trying to drive up any grade though. The advice was to air down the tires but I didn't bother.

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2013 X5 3.5i M Sport
2004 M3 cabriolet SMG