CDs make great plastic wheels if you have plastic inserts to fit inside the center hole. The inserts fit a 1 ⁄4-inch dowel. Since these are much larger than the other wheels, cars using them can roll easily. The Web site sells plastic inserts, and your postal carrier probably delivers free CDs, such as those offering Internet services. A pine board with one-inch by four-inch sideboards (to keep cars from falling off the edge) makes a great ramp. To reduce the gap between the ramp and floor, plane or rasp wood off the bottom edge of the ramp. Cardboard, reinforced with strips of cardboard, also works. Prop.
