Motorcycle transmissions use a series of internal and external parts to maintain an ideal RPM range. These include:
- Bearings: Pressed into the outer engine or transmission case, bearings allow the transmission shafts to spin free and true.
- Input/main shaft: Driven by the engine via the clutch pack, the input/main shaft is how the transmission receives power.
- Output/countershaft: Driven by the main shaft, the output/countershaft delivers power to the final drive via a sprocket or driveshaft.
- Gears: Motorcycle transmissions have three gear types - fixed, freewheeling and slider. Two constantly meshed gears make up each gear ratio, meaning a six-speed transmission will have 12 gears. See more on the types of gears and related mechanisms below:
- Fixed gears are part of, or locked to, the main shaft or countershaft and rotate at the same speed.
- Freewheeling gears spin independently of the main shaft or countershaft. They have dogs (protrusions) or slots on their sides so they can engage with a neighboring gear.
- Slider gears spin with the shafts (main or counter); however, they are free to move horizontally on the shaft. As they slide to engage their neighboring freewheeling gear, they make the freewheeling gear temporarily fixed.
- Shift fork: The shift fork(s) control the horizontal movement of the slider gears.
- Shift drum: The shift drum controls the movement of the shift forks.
- Shift linkage: The shift linkage connects the foot-controlled gear selector to the shift drum. As a rider moves the gear selector up or down, the shift linkage rotates the shift drum, causing the shift forks to move slider gears to engage with their neighboring freewheeling gear.
