A retractable wheel system includes a rotatable member, a swing arm attached to the rotatable member and a wheel, a swing mount attached to the rotatable member, and a spring member. The spring member is attached to the swing mount at a connection point on a first end and to the swing arm on a second end. The spring member is rotatable relative to the swing mount at the connection point. The spring member is configured to apply a force in an upward direction when the connection point is above a line extending between a wheel attachment point and a swing arm rotation point of the swing arm and a force in a downward direction when the connection point is below the line of the swing arm. A transportation unit including the retractable wheel system is also disclosed.
