What is often referred to as Duchamp's first readymade (made two years before Duchamp even solidified the term "readymade") was his Bicycle Wheel of 1913, which is basically a bicycle wheel (note: with no tire on it) that turns if spun and is mounted upside-down into a draughtsman’s stool.
According to Duchamp, it was not art, but just something to have in a room, much like a pencil sharpener. In retrospect, Duchamp also saw Bicycle Wheel as a transitional or experimental work that came between his more “clearly established” readymades of later years and his previous paintings. This was primarily because it was a work that could be interacted with, i.e. the wheel could be spun. It also was a combination of objects rather than one object by itself, which characterized his later readymades.
One might think of the Bicycle Wheel as helping Duchamp spawn his later ideas. He spoke of the work as being about “simply letting things go by themselves." Additionally, he explained, “To see that wheel turning was very soothing, very comforting, a sort of opening of avenues on other things than material life of every day. I liked the idea of having a bicycle wheel in my studio. I enjoyed looking at it, just as I enjoyed looking at the flames dancing in a fireplace."