Ball-type rear towbar bicycle frame. Many vehicles can be equipped with a 50mm diameter trailer ball at the rear. This is the European universal trailer ball standard. The role of the trailer ball is not only to tow motor homes, motorboats or other equipment, but also to carry the bicycle frame. It is usually installed on high-end SUVs, MPVs or high-end business vehicles, and is popular with business people and women customers.

The frame is generally made of ordinary carbon copper pipes through welding and combination. In order to reduce the weight of the pipe and improve the strength, high-grade bicycles are made of low-alloy steel pipes. In order to reduce the resistance of fast driving, some bicycles also use streamlined steel pipes.