A slider window assembly for a vehicle includes a frame portion having an upper rail and a lower rail and a pair of spaced apart generally vertical frame members, and at least one fixed window panel and a movable window panel. The upper rail includes an upper channel for movably receiving an upper region of the movable window and the lower rail includes a lower channel for movably receiving a lower region of the movable window. The upper rail has a depth dimension that is greater than a depth dimension of the lower rail. The generally vertical frame members are tapered so that the end regions have depth dimensions that are similar to the depth dimensions of the respective rail. The generally vertical frame members have upper attachment portions that are generally wedge-shaped and are configured for press fit attachment at correspondingly formed recesses established at the upper rail.