In one aspect, a dishwasher includes a tub at least partially defining a treating chamber and defining an access opening, a dishrack, and a guide rail assembly slidably mounting the dishrack to the tub. The guide rail assembly has a guide rail mounted to the dishrack or to the tub and has upper and lower tracks, which are spaced from each other by a predetermined height, and at least one pair of wheels comprising upper and lower wheels, which are rotatably mounted to the other of the dishrack or the tub.