Air-cooled motorcycles rely on the natural flow of air to dissipate heat from the engine, while liquid-cooled motorcycles use a radiator to circulate coolant and transfer heat away from the engine. Air-cooled motorcycles do not have a radiator, as they do not use a liquid coolant system.
Liquid-cooled motorcycles have a radiator because the coolant needs to be cooled before it can be recirculated through the engine. The radiator is typically mounted in front of the engine and is made of thin metal tubes that allow air to flow through them. As the coolant flows through the tubes, it is cooled by the air flowing over them.