The ornamental design for a frame of a balancebike, as shown and described.
FIG. 1 is a front and left side perspective view of a frame of a balance bike, embodying my new design;
FIG. 2 is a left side elevation view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a rear elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a front and left side perspective view thereof as installed on an exemplary balance bike.
The broken line showing of the balance bike is provided for the purpose of illustrating environmental structure and form no part of the claimed design.