Abstract: A wheel assembly has a wheel holder seat having a hollow pivot end and two lugs, and a main seat having a reinforced main body, a hollow pivot cover, a notch, two inner flanges, an inner interior, and a post. The wheel holder seat has two laterals engaging with the inner flanges. A push rod has an upper recess hole. The push rod is inserted in the inner interior. A coiled spring has a lower portion inserted in the upper recess hole and an upper portion enclosing the post. The hollow pivot end is inserted in the hollow pivot cover. A pivot shaft fastens the hollow pivot cover and the hollow pivot end together. A pivot pin fastens a wheel between two lugs.