Miracle Casters use wheels that are nearly 4 inches in diameter. That's twice the diameter of the cheap casters supplied on 99 percent of all office chairs sold in the U.S. Because of their larger size, Miracle Casters roll easily over thick carpet, and are less likely to get bogged down on padded carpet. Remember the huge wheels on horse-drawn wagons? Miracle Casters work on the same principle. The bigger the wheel, the easier it will roll over a soft or uneven surface.