text: what is the difference in inches between the length of the spokes of the two wheels? the diameter of one bicycle wheel is 28 inches and its spokes run from the hub (or center) to the edge of the rim. the diameter of another bicycle wheel 21 inches. what is the difference in inches between the length of the spokes of the two wheels? three and a half the difference in diameter is seven inches, and you are asking the difference in radius, which is half the diameter.