An adjustable supporting bracket for a motorcycle backrest that may be disposed between a mounting bracket affixed to a motorcycle seat and a mounting bracket affixed to a backrest pad. The adjustable supporting bracket comprises an outer member and an inner member slidingly received within the outer member. The inner member has a hand retractable spring plunger whose tip is disposed to engage longitudinally arrayed recesses in the outer member in order to lockably fix the extension of the inner member. One of the outer member and the inner member is also provided with a tilt wheel disposed within a transverse slot in a lower portion of the member. The tilt wheel is threaded to receive a set screw that extends through the lower portion of the member to bear against the seat mounting bracket. The tilt wheel may be manually rotated to extend and retract the set screw, thereby allowing the user to determine the extent of backward travel of the backrest.