Concept of Torque (Speed) Variation in Transmission System: When two different size gears are running at same speed, then the small gear makes more revolution than the big gear. This means the speed ratio can vary with the gear size.
The same principle is applied in the speed variation of motorcycle. When smaller gear on the main shaft is in mesh with larger gear on the counter shaft, the revolutions of the counter shaft will be lesser than the main shaft, because the larger gear mounted on countershaft will make less revolution than the smaller gear mounted on main shaft.
The transmission system mainly consists of clutch, gears and drive chain. (Diagrammatic representation of a transmission system), a clutch is mounted on the main shaft of the gear box. A primary drive gear mounted on main shaft of the engine drives the driving shaft of the clutch through primary driver gear while the driver shaft of the clutch is connected to the main shaft of the gear box. The drive chain connects the counter shaft and rear wheel. The power is transferred from the main shaft to the counter shaft through various gears and then to the rear wheel through a drive chain.
A higher torque is required to bring the motorcycle into running condition from stationary state but when the motorcycle is running at high speeds the torque required is less.