What is "Bore" in a Bike?

"Bore" in a motorcycle refers to the diameter of the cylinder in the engine block, which is the part of the engine where the combustion of fuel and air takes place. The bore is one of the two primary measurements that determine an engine's displacement, the other being the stroke.

The bore is measured in millimeters (mm) or inches (in) and is the distance between the inner walls of the cylinder, usually at its widest point. It's important to note that the bore diameter is different from the piston diameter, which is slightly smaller and fits inside the cylinder.

The size of the bore is a crucial factor in determining an engine's power and torque output. Generally, a larger bore allows for a larger displacement engine, which can produce more power and torque. However, increasing the bore size also increases the amount of friction between the piston and cylinder walls, which can affect the engine's efficiency and longevity. Therefore, bore size is usually balanced against other factors such as the stroke length, valve size, and compression ratio to achieve the desired performance characteristics.

Bore size is also a factor in determining the type of engine, such as whether it is a two-stroke or four-stroke engine. Two-stroke engines usually have a larger bore diameter than four-stroke engines of the same displacement, which contributes to their higher power-to-weight ratio but also makes them less fuel-efficient and more polluting.