The EasyFold XT 3 is designed to carry a maximum of 3 bikes with a total load capacity of 60 kg. It does not support an add-on for a 4th bike. It is compatible with the ABUS lock system as it features lockable bike-to-rack and rack-to-vehicle functions, and is One Key System compatible. However, there is no official add-on for a 4th bike for this model.