When you're ready to double up the excitement, effortlessly add up to two extra riders using a 1-Bike or 2-Bike Add-On for the Kuat Piston Pro Bike Rack . The user-friendly modular design makes attaching the additional trays a no-brainer. FEATURES: 1-Bike add-on reduces the capacity to 50lbs per tray 2-Bike add-on reduces the capacity to 40lbs per tray Add-On racks are not rated for use on an RV