Clutch: Clutch is a part which is used to transmit the rotary motion of one shaft to another shaft, when desired; the axis of second shaft must be in line with the axis of the first shaft (coaxial). The clutch in the motorcycle works on the principle of friction. When a rotating disc comes in contact with other disc, then by the virtue of friction of these plates, both the discs rotate as a single unit.
The clutch may be wet or dry. A wet clutch runs with oil but a dry clutch is not lubricated. A wet clutch will run cool. Further, the clutches may have flat or conical contact surfaces.
In a single plate clutch, contact may be made on two sides while in case of multiple clutches several plates make contact. The other types are semi-centrifugal and centrifugal clutches.
Multi plate clutches are used in motorcycles since they require less radial space.