A rotor blade, comprising: a spar comprising an internal space extending to a tip end of the spar; and a weight system (200; 300; 400) for a rotor blade, the weight system being disposed within the internal space, the weight system comprising: a weight box (202; 302; 402) open in a spanwise direction; wherein the weight box (202; 302; 402) is bonded to the spar; a weight guide rod (212; 312; 412) connected to the weight box, the weight guide rod extending in a spanwise direction through an interior of the weight box; and a span balance weight (206; 306; 406) disposed within the weight box, the span balance weight being captured between the weight guide rod and the weight box; wherein the span balance weight is configured for insertion into the weight box and removal from the weight box via the tip end of the spar and the spanwise direction opening of the weight box; characterized in that the weight box is extending both forward and rearward relative to a pitch change axis of the spar; and the tip end of the spar is offset spanwise in an inboard direction from an end cap of a tip end of the rotor blade; and the weight box is connected to the spar using fasteners and wherein the fasteners are flush with an exterior of the spar or recessed relative to the exterior of the spar. a spar comprising an internal space extending to a tip end of the spar; and a weight system (200; 300; 400) for a rotor blade, the weight system being disposed within the internal space, the weight system comprising: a weight box (202; 302; 402) open in a spanwise direction; wherein the weight box (202; 302; 402) is bonded to the spar; a weight guide rod (212; 312; 412) connected to the weight box, the weight guide rod extending in a spanwise direction through an interior of the weight box; and a span balance weight (206; 306; 406) disposed within the weight box, the span balance weight being captured between the weight guide rod and the weight box; wherein the span balance weight is configured for insertion into the weight box and removal from the weight box via the tip end of the spar and the spanwise direction opening of the weight box; characterized in that the weight box is extending both forward and rearward relative to a pitch change axis of the spar; and the tip end of the spar is offset spanwise in an inboard direction from an end cap of a tip end of the rotor blade; and the weight box is connected to the spar using fasteners and wherein the fasteners are flush with an exterior of the spar or recessed relative to the exterior of the spar. a weight box (202; 302; 402) open in a spanwise direction; wherein the weight box (202; 302; 402) is bonded to the spar; a weight guide rod (212; 312; 412) connected to the weight box, the weight guide rod extending in a spanwise direction through an interior of the weight box; and a span balance weight (206; 306; 406) disposed within the weight box, the span balance weight being captured between the weight guide rod and the weight box; wherein the span balance weight is configured for insertion into the weight box and removal from the weight box via the tip end of the spar and the spanwise direction opening of the weight box; characterized in that the weight box is extending both forward and rearward relative to a pitch change axis of the spar; and the tip end of the spar is offset spanwise in an inboard direction from an end cap of a tip end of the rotor blade; and the weight box is connected to the spar using fasteners and wherein the fasteners are flush with an exterior of the spar or recessed relative to the exterior of the spar.