Kuat Piston Pro Add On - Rack - Add On - 2 Bike - Black1 Bike Add On: Quick change from 2 to 3 bikes 2 Bike Add On: Quick change from 2 to 4 bikes Quick change from 2 to 3 bikes or up to a max capacity of 4 bikes 1 Bike Add On holds up to 22kgs per tray 2 Bike Add On holds up to 18kgs per tray Wheelbases up to 135cm, tires as large as 5" Compatible with 2 Piston Pro Compatible with Pivot v2 Only one add on can be used at a time