A wheel rim accessory assemblable to a wheel of a vehicle, including: (a) a casing having an outlet adapted to be in fluid communication with the internal volume of the wheel, the casing being assemblable to the wheel rim of the wheel; (b) a filler substance disposed within the casing; and (c) a valve mechanism operationally coupled with the outlet, the valve mechanism controlling a flow of the filler substance from the casing to the internal volume of the wheel such that when a pressure level in the internal volume of the wheel is below a first predefined level, the valve mechanism allows the filler substance to flow into the internal volume until the pressure level reaches a second predefined level, wherein the second predefined level is equal to, or greater than, the first predefined level.