It depends on the plane. Many planes where the wheels are in the same position from the leading edge whether the gear is up or down, then it doesn't matter because the CG doesn't change. But when you have a plane where the retract is out by the leading edge and the wheels rotate up towards the center of the wing like a "Skyraider" you need to be checking the CG with the gear up and the weight of the tires further back. The same holds true for a tricycle gear, the weight of the gear is further back in the retracted gear and that is where you need to check the CG. JMPUPS