^What keeps the bikes from tipping over? I've been thinking about doing something similar with cabinets/drawers underneath to store helmets, shoes, pump, etc.

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I've had this half-baked idea floating around my head to modify a display rack from a rug store. The kind where you can browse through rugs like turning pages of a book. They are quite sturdy, usually made of steel tubing, and tall enough to hang bikes from one wheel. Add some hooks and then you could flip through your bikes to decide which one you'd use that day.