Rack assembly

A rack assembly comprising:

• two side racks spaced from each other;
• two rails mounted between and connected with the side racks, being parallel with each other, located at a same height, and including a front rail and a rear rail, and each rail having a U-section to form an opening in a bottom of the rail, wherein
• each rail comprises a bottom panel, an outer panel, and an inner panel;
• the outer panel and the inner panel are respectively formed on and extend downwardly from two sides of the bottom panel;
• the inner panels of the two rails face each other;
• and
• the inner panel has a downward extension length larger than a downward extension length of the outer panel;
• and
• at least one sub-rack disposed between the side racks, being slidable along the rails, and each one of the at least one sub-rack comprising
• a rack frame composed of multiple longitudinal rods, which include at least one front rod and at least one rear rod corresponding in position respectively to the front rail and the rear rail, wherein each one of the at least one front rod has
• an extension rod mounted retractably on a top of the front rod and having a front wheel mounted rotatably on a top of the extension rod;
• and
• a spring mounted in the front rod and abutting a bottom of the extension rod to push the extension rod upward and to hold the front wheel on the extension rod in the front rail;
• a connection rod connected to the extension rod of each one of the at least one front rod;
• and
• at least one supporting member mounted on the rack frame.