Expands MonoRail 2" receiver model to carry 3 bikes or MonoRail Solo to carry 2 bikes Lowers max weight capacity from 60 lbs to 45 lbs per tray No frame contact Carries road tires up to 5.0" fat tire bikes and diameters from 20" to 29" Compatible with wheelbases from 36" to 50" Third party online sales strictly prohibited by manufacturer