No, not all motorcycles have fins. Fins are typically found on certain types of motorcycles, especially those designed for specific purposes such as racing or high-performance bikes. Fins are often used for heat dissipation to help cool the engine or other components by increasing surface area for better airflow. They can be seen on some sport bikes, superbikes, and even some cruiser-style motorcycles.
These bikes may have alternative methods of cooling, such as liquid cooling systems, which don't require the use of fins. Additionally, some motorcycles may have cosmetic fins for aesthetic purposes rather than functional ones.
It's important to note that motorcycle designs can vary significantly, and while fins are a common feature on certain types of bikes, they are not universal to all motorcycles.