Disclosed is a knockdown shelving system which comprises a plurality of connected shelves with storage compartments that are configured to store vehicle wheels or tires upright and parallel to each other. Vertical posts are located at each corner of the connected shelves and shared between adjacent shelves. The vertical posts are formed of a rolled hollow T-profile which comprises rows of longitudinally spaced perforations that extend along the vertical posts. The vertical posts are connected by lengthwise and crosswise struts, the struts having hooks which engage the perforations of the vertical posts. Storage compartments for tires or wheels are formed by tire carriers which are placed onto lengthwise struts and extend parallel between front and rear vertical posts, and by crosswise struts which extend perpendicular to the tire carriers between two front vertical posts and two rear vertical posts, respectively.